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Showing papers in "Journal of Non-crystalline Solids in 1973"


Journal ArticleDOI
TL;DR: In this paper, an equation for direct calculation of the Young's modulus of oxide glasses from their chemical compositions is derived based on a consideration of dissociation energy of the oxide constituents per unit volume and the packing density.
Abstract: An equation has been derived for the direct calculation of the Young's modulus of oxide glasses from their chemical compositions. The method is based on a consideration of dissociation energy of the oxide constituents per unit volume and the packing density. For borate glasses, the ratio of four-coordinated to three-coordinated borons must be taken into consideration. Excellent agreement is obtained between calculated and measured values of Young's modulus for over thirty different glasses.

615 citations


Journal ArticleDOI
TL;DR: In this article, the behavior at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours.
Abstract: Dc conductivity measurements have been made between 90 and 520 K on three bulk samples of V 2 O 5 P 2 O 5 glass. Heat treatment is found to result in a reduction of the activation energy at a given temperature and this is most noticeable at low temperatures. The behaviour at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours. At intermediate temperatures a simple model is used in which excitations by optical and acoustic phonons are considered to make independent contributions to the jump frequency. Mott's theory is extended to the polaron case for T> 1 4 ⊖ and is shown to be in good agreement with results. Values for r p (∼2.8 A ) the polaron radius and α(∼3.5 A −1 ) the electron decay constant are shown to be consistent with the model for small polarons. A method is suggested for obtaining α and N ( E F ) from the ac conductivity and the slope of 1nσ versus 1 T 1 4 at low temperatures. Values of N ( E ) are obtained which correlate with those obtained by the previous analysis. This implies that the disorder energy separating adjacent sites Δ 0 is large (∼0.4 eV) in these materials.

285 citations


Journal ArticleDOI
TL;DR: In this paper, the photoconductivity and absorption of Si specimens were measured at room temperature as a function of photon energy and Td in a spectral range from 0.5 eV to 3 eV and the absorption coefficient was determined for evaporated, sputtered and glow discharge specimens.
Abstract: The paper deals with photoconductivity and absorption in aSi specimens, prepared mainly by the decomposition of silane in a glow discharge. Substrate temperatures, Td, between 300 K and 650 K were used during deposition. The normalised photoresponse was measured at room temperature as a function of photon energy and Td in a spectral range from 0.5 eV to 3 eV. The absorption coefficient was determined for evaporated, sputtered and glow discharge specimens. The main features of the results are in agreement with conclusions drawn from previous electrical transport and field effect measurements and can be interpreted on the basis of the proposed model for the localised state distribution. It is confirmed that ϵc−ϵv is 1.5 to 1.6 eV, and that there is a local density of state maximum at about 1.2 eV below ϵc. At room temperature the steady photocurrent is carried predominantly by electrons in states above ϵc, whether excitation is from localized or extended states. Specimens prepared at Td > 500 K are highly photosensitive, with electron recombination lifetimes, τ, of up to 10−5s. Rise and decay times of the signal lie in the millisecond range. For Td < 500 K there is a drastic decrease in τ, which falls to 10−11 s at Td ⋍ 300 K and is even less for evaporated specimens. These results are discussed in some detail.

186 citations


Journal ArticleDOI
TL;DR: In this article, a model describing the structure of amorphous metallic alloys is proposed using a packing of non-equal-sized hard spheres, and the radial distribution function and the interference function are calculated for each model and the variations of these curves with the number of spheres are studied.
Abstract: A model describing the structure of amorphous metallic alloys is proposed using a packing of non-equal-sized hard spheres. Models containing up to 1000 spheres were generated by computation. Hypotheses guiding the calculation are chosen in order to obtain a model as compact as possible and to take into account affinity between metal and metalloids: therefore two small spheres are not allowed to be in hard contact. This method of calculation is first tested by building up heaps of equal-sized spheres. Both the radial distribution function and the interference function are calculated for each model and the variations of these curves with the number of spheres are studied. In the case of two sizes of spheres heaps calculations are devoted to the study of the so-called ‘shoulder interference function’ which characterizes many amorphous alloys such as NiP, PdSi, etc. It is shown that the existence of such a shoulder depends on two parameters: the ratio of sphere diameters and the relative concentration of small and large spheres. These results are in good agreement with some recent experimental observations. This shoulder is well-marked when the diameter ratio reaches 10% and when the concentration in small spheres lies in the range 10–15%. In such a structure (e.g. amorphous NiP and PdSi alloys) it is observed that small spheres are always surrounded by nine large spheres such as P or Si atoms in crystalline Ni3P or Pd3Si. Large spheres, i.e. metallic atoms, form distorted icosahedra, the distortion of which varies from one to the other. The short-range order has a five-fold symmetry which is not compatible with any long-range order.

181 citations


Journal ArticleDOI
TL;DR: In this paper, the compatibility of electronic and ionic conduction processes in glasses such as Ag-doped As-Se glasses and Bi2O3B 2O3 glass was discussed from these aspects.
Abstract: Electrical conduction in various inorganic glasses was studied as a function of hydrostatic pressure up to 2000 atm and phenomenologically classified into electronic, ionic and mixed types. In electronically conducting glasses such as AsSe chalcogenide glasses and Fe2O3P2O5 glass, the conduction is enhanced by application of pressure. On the other hand in ionically conducting glass such as Na2OB2O3 glass, the conduction is suppressed through the concept of an activation volume. The compatibility of electronic and ionic conduction processes in glasses such as Ag-doped AsSe glasses and Bi2O3B2O3 glass, which have more complex conduction processes, was discussed from these aspects.

132 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the rate of crystal nucleation in alkali disilicate glasses by counting the number of crystals under an optical microscope and measured the viscosities of these glasses by the method of beam bending and penetration using the data of rate of nucleation and viscosity obtained in the present study and data of free energy measured by Takahashi and Yoshio.
Abstract: Rates of crystal nucleation in alkali disilicate glasses were measured by counting the number of crystals under an optical microscope The viscosities of these glasses were measured by the method of beam-bending and penetration Using the data of rate of nucleation and viscosity obtained in the present study and the data of free energy measured by Takahashi and Yoshio, crystal-glass interfacial energies for alkali disilicate systems were estimated on the basis of homogeneous nucleation theory as follows: 196 erg/cm2 for Li2O·2SiO2, 126–144 erg/cm2 for Na2O·2SiO2 and 88–104 erg/cm2 for K2O·2SiO2 The effects of the viscosity of glass, the free energy difference between crystal and glass and crystal-glass interfacial energy on the rate of nucleation were discussed, and the remarkably higher rate of crystal nucleation in the Li2O·2SiO2 glass was attributed to the larger free energy difference

100 citations


Journal ArticleDOI
TL;DR: In this article, the Fourier transform was used to measure the properties of As-Te 3/2 units, which are interconnected through As-As locks, and it was shown that these locks play a crucial role in the stability of the As-rich glasses in favoring strongly the covalent bonds.
Abstract: Diffraction measurements on bulk and thin films AsTe glasses are reported, throughout the whole range of stability. FNP distances and areas, average valence angles and compactness are determined from the Fourier transform. For As-rich glasses important differences are found between short-range order in both vitreous and crystalline states. An interpretation at the molecular scale is proposed. It takes account of the particular topological properties of the AsTe molecules, which are evidenced by hand-made models. The proposed structure consists of a network of AsTe 3/2 units which are interconnected through “AsAs locks”. It is shown that these “locks” play a crucial role in the stability of the As-rich glasses in favoring strongly the covalent bonds. On the other hand, in Te-rich glasses there is no similar locking mechanism. The presence of threefold-coordinated tellurium sites enhances the metallic character, and weakens the difference between crystalline and vitreous states. The structural models which are proposed enable us to explain the anomalies and the discontinuities of most thermodynamic properties which are described in paper I.

86 citations


Journal ArticleDOI
TL;DR: In this article, the diffracted X-ray intensities, F ( k )'s, and radial distribution functions of Ge, some III-V compounds, and Ge 0.5 Sn 0.
Abstract: The diffracted X-ray intensities, F ( k )'s, and radial distribution functions of Ge, some III–V compounds, and Ge 0.5 Sn 0.5 are presented. It is shown that the radial distribution functions of the III–V compounds are similar to those of Ge. If the continuous random network, as developed for amorphous Ge, is also applicable to the III–V's, then several bonds between like atoms (wrong bonds) must be present. It is argued that the energy of wrong bonds may not be sufficiently high to prohibit their formation.

86 citations


Journal ArticleDOI
TL;DR: In this article, a novel reversible change in the optical property, transmission and refractive index, due to light irradiation has been found in the As-Se-Ge glass film, which makes the material suitable for erasable (optical) memory medium.
Abstract: A novel reversible change in the optical property, transmission and refractive index, due to light irradiation has been found in the AsSeGe glass film. The change is not related with a usual amorphous-crystalline type transformation; a weak lightr causes an edge shift to longer shorter wavelengths also occur upon heating the sample, which suggests that the shift du to the strong light irradiation is originated from the “heating effect” of light. This was confirmed by an experiment with a sample coated with metal-smoke. The change of optical transmission during the weak light irradiation was measured; it is decreased exponentially with time, and the rate of decrease became larger as the power of irradiationg light increased. Good reversibility of the optical transmission was obtained, which makes the material suitable for erasable (optical) memory medium.

75 citations


Journal ArticleDOI
K. Tanaka, Y. Okada, M. Sugi, S. Iizima, M. Kikuchi 
TL;DR: In this paper, a simplified model of the ionic behavior of the constituent elements in switch-on plasma was proposed to explain the polarity dependence of the filament growth, and a strong correlation between the waiting time and the crystallization rate has also been indicated for their dependences on both the composition of the glass and the temperature.
Abstract: Memory (lock-on) phenomena observed in semiconducting glasses of the AsTeGe system have been investigated by electrical, calorimetrical and X-ray methods. Some differences between the memory process observed in high-As glasses and that in low-As glasses have been shown, which include both the waiting time for the process and the growth behaviour of the conductive filament formed between the electrodes. A strong correlation between the waiting time and the crystallization rate has also been indicated for their dependences on both the composition of the glass and the temperature. Finally, the kinetics of growth of the conductive filament during the memory process has been discussed using a simplified model, based on the ionic behaviour of the constituent elements in switch-on plasma, which explains well the polarity dependence of the filament growth.

75 citations


Journal ArticleDOI
TL;DR: In this paper, a coherent analysis of all the data is developed which shows that important differences of local order exist between amorphous and crystalline states and also between the two well-distinct types of glasses we are dealing with.
Abstract: AsTe glasses have been investigated for determining the molecular mechanisms of glass formation and of crystallization. Stable and homogeneous bulk glasses are prepared throughout the range of concentration from 20 to 65 at % As, by using an improved quenching method. GFA (glass-forming ability) is determined with respect to the rate of cooling. Density, microhardness, T g and ΔC p at T g are measured in the whole range of glass formation. Finally a quantitative analysis of the kinetics of crystallization is carried out. It appears that most properties which involve molecular motions exhibit anomalies for As 40 Te 60 composition (As 2 Te 3 is the unique definite compound of the system). So GFA shows a sharp depression for this critical composition; similarly enthalpy and kinetics of crystallization are drastically modified at As 40 Te 60 . For Te-rich glasses, crystallization occurs at low temperature by homogeneous nucleation with a small energy of activation. For As-rich glasses, crystallization occurs at much higher temperatures. Above 200°C it is controlled by growth with an high activation energy which indicates deep rearrangements of the relative positions of the atoms by chemical diffusion. A coherent analysis of all the data is developed which shows that important differences of local order exist between amorphous and crystalline states and also between the two well-distinct types of glasses we are dealing with. The aim of paper II is to determine these differences from diffraction data.

Journal ArticleDOI
TL;DR: In this article, the importance of non-crystalline SiO2 films in the manufacture of semiconductor devices and integrated circuits is pointed out; a properly prepared interface is very perfect.
Abstract: Firstly, the importance of noncrystalline SiO2 film in the manufacture of semiconductor devices and integrated circuits is pointed out. After some general remarks on the SiSiO2 interface, various methods of preparing SiO2 films on silicon are discussed with emphasis on thermal oxidation of silicon. The transport processes are compared with those occurring in fused silica. Then, the properties of the SiSiO2 interface structure are summarized; a properly prepared interface is very perfect. This is due to the structural flexibility of noncrystalline SiO2. Finally, the structural aspects of noncrystalline SiO2 are discussed on the basis of the chemistry of the SiO bond in which the π component plays a special role. The high degree of short-range order is responsible for many excellent properties of the oxide film. Disruption of the short-range order results in network defects and development of some degree of local order along a direction which it is assumed to give rise to channels. These defects are unique to topologically disordered solids. In this and many other respects, noncrystalline SiO2 is more similar to siloxane polymers than typical ionic or covalent crystals.

Journal ArticleDOI
TL;DR: In this paper, the internal friction of sodium metaphosphate glasses containing from 0.016 to 0.330 wt% water has been investigated and a mechanism consisting of the cooperative motion of sodium ions and protons has been proposed for this peak.
Abstract: The internal friction of sodium metaphosphate glasses containing from 0.016 to 0.330 wt% water has been investigated. Weight loss and infrared absorption measurements were used to determine the water content. Of the two internal friction peaks observed between −100°C and ∼250°C, the second peak occurring above room temperature has a pronounced dependence upon the water content; increasing water content causing the activation energy to decrease as the peak increased in size. A mechanism consisting of the cooperative motion of sodium ions and protons has been proposed for this peak. It is concluded that the second peak in the NaPO 3 glasses and the similar peak in alkali silicate glasses is not associated with the movement of the non-bridging oxygen ions.

Journal ArticleDOI
TL;DR: In this article, the optical and electrical properties of PbO-SiO 2 glasses containing 24.6 to 65 mole % pbO have been determined, and an abrupt lightening in color is observed in the vicinity of 38-40% Pb O. The origin of this scattering is tentatively identified with the formation of microcrystals of SiO 2 in the glasses.
Abstract: The optical and electrical properties of PbO-SiO 2 glasses containing 24.6 to 65 mole % PbO have been determined. While the short-wavelength cutoff increases continuously in wavelength with increasing PbO concentration, an abrupt lightening in color is observed in the vicinity of 38–40% PbO. The darker color of glasses containing 30–38% PbO has been associated with a scattering process. The origin of this scattering is discussed and is tentatively identified with the formation of microcrystals of SiO 2 in the glasses. The alternative process of liquid-liquid phase separation seems less likely, but cannot be ruled out with certainty. The electrical conductivity of all glasses investigated exhibits an Arrhenian temperature dependence. The activation energy decreases from about 1.23 eV for the 30% PbO composition to about 1.11 eV for the 50% PbO composition, and remains about constant for glasses containing higher concentrations of PbO. Addition of NH 4 Cl or Sb 2 O 3 to the batch or use of Pb(NO 3 ) 2 or Pb 3 O 4 instead of PbO as a raw material does not affect the electrical properties. The dielectric constant at 1kHz increases continuously with increasing PbO concentration, from a value in excess of 20 for the 55% PbO composition. The implications of these results for the conduction mechanism in PbO-SiO 2 glasses are discussed.

Journal ArticleDOI
TL;DR: In this paper, the electrical properties of glasses in the Na2OP2O5, Ag2O-P 2O5 and P2O 5 systems have been measured over a range of temperature and composition.
Abstract: The electrical properties of glasses in the Na2OP2O5, Ag2OP2O5 and (1−x)Na2OxAg2OP2O5 systems have been measured over a range of temperature and composition. The properties of the Na2OP2O5 and Ag2OP2O5 glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1−x)Na2O−xAg2O−P2O5 system was found around the mole ratio of 0.16:0.84 Ag2O:Na2O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the Tg-against-composition plots. A linear relationship was noted for the tan δ-versus-log10 (resistivity) plot, as has been seen in other glass-forming systems.

Journal ArticleDOI
TL;DR: In this paper, the densification behavior of a number of alkali silicate glasses has been investigated using a Bridgman anvil high pressure device, where the pressure range of the investigation was 10 to 60 kilobars; the temperature range was 100 to 400°C.
Abstract: The densification behavior of a number of alkali silicate glasses has been investigated using a Bridgman anvil high pressure device. The pressure range of the investigation was 10 to 60 kilobars; the temperature range was 100 to 400°C. In all cases, the densification was found to increase with increasing temperature and pressure. In the two systems where compositional variations were explored, Na2OSiO2 and K2OSiO2, a pronounced maximum in densification in the vicinity of 10 mole % alkali oxide was observed (for a given temperature and pressure). These maxima are taken to reflect a competition between two processes, one of which — the variation of molecular mobility with composition — should lead to increasing densification with increasing alkali concentration. Several possibilities are discussed for the decrease in densification with alkali oxide concentrations greater than about 10% (to values smaller than that of SiO2 in some cases). The present results are related to those obtained in previous investigations of the densification of oxide and polymeric glasses.

Journal ArticleDOI
TL;DR: The best glass formers were in the Nb2O5-and Ta2O3-based systems as mentioned in this paper, where the indices of refraction of most of the glasses and Abbe numbers of many were measured.
Abstract: Glass spherules have been made by laser spin melting and free fall cooling techniques from ceramic rods. Thus, the materials were not in contact with a container at any time. Glasses of 100 to 800 μm diameter were formed from at least 80 wt% of the oxides Al2O3, Ga2O3, In2O3, La2O3, ZrO2, HfO2, Nb2O5 and Ta2O5 with 20 or less weight percent of CaO + SiO2. The best glass formers were in the Nb2O5- and Ta2O5-based systems. The indices of refraction of most of the glasses and Abbe numbers of many were measured.

Journal ArticleDOI
TL;DR: A series of semiconducting samples with non-crystalline structure was prepared by the thermal degradation of phenol formaldehyde resin at different heat treatment temperatures as discussed by the authors, and DC measurements on these organic materials yield an interesting extension of the existing knowledge about the amorphous state.
Abstract: A series of semiconducting samples with noncrystalline structure was prepared by the thermal degradation of phenol formaldehyde resin at different heat treatment temperatures. DC measurements on these organic materials yield an interesting extension of the existing knowledge about the amorphous state. The most important result is the fact that pyrolyzed phenol formaldehyde resins show a temperature dependence on conductivity which is characteristic for the Mott hopping mechanism and identical with that of layers made by evaporating Ge, Si, GaAs or carbon. Hence it does not seem to be the chemical composition that is determining the mechanism of electrical conduction in amorphous solids but only the physical structure.

Journal ArticleDOI
TL;DR: The viscosity of 99.99% pure selenium has been determined over the available range of temperature where crystallization could be avoided as discussed by the authors, and the critical stress for non-Newtonian flow was found to lie in the range of hundreds of psi, which was appreciably smaller than that for oxide liquids in a similar range of viscosities.
Abstract: The viscosity of 99.99% pure selenium has been determined over the available range of temperature where crystallization could be avoided. A bending beam viscosimeter was used to obtain data in the high viscosity region, and a rotating cylinder instrument was employed for the low viscosity range. Also determined was the stress dependence of the viscosity at temperatures of 31.5 and 29.6°C. The critical stress for non-Newtonian flow was found to lie in the range of hundreds of psi, which is appreciably smaller than that for oxide liquids in a similar range of viscosity.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the bleaching of bulk titania-silica glasses in the annealing temperature range and showed that the sample-size kinetics can be predicted from the hydrogen diffusion coefficient.
Abstract: The bleaching of bulk titania-silica glasses in the annealing temperature range is investigated. The sample-size kinetics can be predicted from the hydrogen diffusion coefficient. Hydrogen gas is evolved from both titania-silica and silica glass but in larger amount from the former. In the bleaching process, Ti 3+ ions disappear from the titania-silica glass. These results are consistent with the coloration caused by Ti 3+ which is oxidized by OH- in the glass to produce gaseous hydrogen.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the ultrasound wave velocity and attenuation in a series of quenched and heat-treated Na2O-B2O3SiO2 glasses and found that the attenuation of both longitudinal and shear waves below room temperature is dominated by a broad and intense loss peak.
Abstract: Measurements of ultrasound wave velocity and attenuation have been made between 1.3 K and 400 K in a series of both quenched and heat-treated Na2OB2O3SiO2 glasses. As in many other inorganic glasses, the ultrasound attenuation of both longitudinal and shear waves below room temperature is dominated by a broad and intense loss peak; the height and temperature of the peak maximum are frequency sensitive. The loss peak characteristics are consistent with a structural relaxation mechanism with a distribution of activation energies and this model is used to analyse the data. The features of the acoustic loss peak and also the absolute value and temperature coefficient of ultrasound velocity are strongly dependent on the total Na2O network modifier content of the glasses. The ultrasound wave propagation is also affected by phase-separation inducing heat treatment: a steady rise in the height of the acoustic loss peak and an upward shift in the peak temperature takes place with increasing time of heat treatment at 550°C, a finding which suggests that structural rearrangements are still occurring in the individual glassy phases even after long periods of heat treatment. It is proposed that heat treatment causes migration of Na+ ions away from BOB bonds in the B2O3 rich phase.

Journal ArticleDOI
TL;DR: In this article, a comparison between a Mossbauer spectroscopy determination and the classical chemical analysis of the Fe/sup 2+/ content in SiO/sub 2/-Na/sub O/sub 3/ glass systems, for different iron concentrations, and for 16.0 and 24.0 wt% Na/sub 1/O respectively is given.
Abstract: A comparison is given between a Mossbauer spectroscopy determination and the classical chemical analysis of the Fe/sup 2+/ content in SiO/sub 2/-Na/sub 2/O-Fe/sub 2/O/sub 3/ glass systems, for different iron concentrations, and for 16.0 and 24.0 wt% Na/sub 2/O respectively. The agreement between Mossbauer analysis and chemical analysis is good only for large Fe/sub 2/O /sub 3/ contents, while for small Fe/sub 2/O/sub 3/ contents the Mossbauer analysis gives a much larger Fe/sup 2+//(Fe /sup 2+/+Fe/sup 3+/) ratio than the chemical analysis: a physical reason is given for this fact. The Fe/sub 2/O/sub 3/ content below which Fe/sup 2+/ becomes predominant in glass is rather sharply defined, and a qualitative explanation is proposed to account for this rapid transition from Fe/sup 3+/ to Fe/sup 2+/.

Journal ArticleDOI
TL;DR: In this paper, the black P structure is used as a model for the structures of amorphous GeS, GeSe and GeTe and the model yields satisfactory agreement with the observed position and area of the second neighbor X-ray radial distribution function peaks.
Abstract: The black P structure is presented as a model for the structures of amorphous GeS, GeSe and GeTe. It is shown that the short interatomic distances, low near neighbor coordinations and high covalencies of the amorphous materials, relative to the crystalline, can be rationalized with the model. When scaled to the near neighbor interatomic distances in the amorphous materials, the model yields satisfactory agreement with the observed position and area of the second neighbor X-ray radial distribution function peaks. The model predicts: (a) A first neighbor peak area for GeS which is significantly different from that predicted by the random covalent model and (b) phase separation in certain composition regions which, for the Ge-S system, should be observable by means of transmission electron microscopy. An explanation of why phase separation is not likely to be observable through transmission electron microscopy studies of amorphous GeTe and GeSe is also presented.

Journal ArticleDOI
TL;DR: In this article, the angular distribution of intensities of an alloy of Ge 0.175 and Te 0.825 in the amorphous and in the liquid state have been measured.
Abstract: The angular distribution of intensities of 1.003 A neutrons scattered by an alloy of Ge 0.175 Te 0.825 both in the amorphous and in the liquid state have been measured. The bulk amorphous sample, prepared by water quenching of the melt, has been examined at room temperature and just above the crystallization temperature T x . The liquid sample has been examined at 400, 600 and 800°C. The analysis of the structure factors obtained from the corrected and scaled intensities indicates that the structural features of the amorphous sample are similar to those which would be expected if it were possible to cool the alloy to room temperature, while maintaining it in the liquid state. The analysis of the radical distribution functions, from Fourier inversion of the structure factors, indicates that a change of the coordination number n 1 from 2.43 to 3.25 occurs in passing from the amorphous to the liquid state at 400°C. This result has been interpreted in terms of coordination models. In the liquid state, it has been found that a model with fourfold coordinated Ge and threefold coordinated Te is consistent with n 1 =3.25. The internal consistency of this model for the liquid state allows us to make a reasonable choice between the possibility of a 3 or 4 fold coordination for Ge in the glass. We conclude that a model based on four-fold coordinated Ge and twofold coordinated Te seems an appropriate representation for the coordination of the amorphous material.

Journal ArticleDOI
TL;DR: The simple micro-crystallite model is used to calculate the diffraction and radial distribution functions for a variety of tetrahedrally coordinated crystal structures as discussed by the authors, including diamond, wurtzite, Ge III and Si III.
Abstract: The simple microcrystallite model is used to calculate the diffraction and radial distribution functions for a variety of tetrahedrally coordinated crystal structures: diamond, wurtzite, Ge III and Si III — two high-pressure polytypes of Ge and Si — and two clathrate structures based on pentagonal dodecahedral units. Comparison with data for sputtered amorphous Ge suggests that the simple microcrystallite model is inadequate to fit diffraction data. A statistical or combination microcrystallite model may be more promising. Recent electron microscopic investigations of Rudee and Howie are also discussed.

Journal ArticleDOI
TL;DR: In this paper, the complete compositional range of the amorphous SbSe system has been prepared in thin-film form by a simple evaporation technique, and optical and transport properties have been measured as a function of composition.
Abstract: Essentially the complete compositional range of the amorphous SbSe system has been prepared in thin-film form by a simple evaporation technique. Optical and transport properties have been measured as a function of composition.

Journal ArticleDOI
TL;DR: In this article, the energy transfer between thulium and erbium was studied and it was concluded that the energy is transferred via the phonons of the host glass, and that the efficiency of energy transfer from thule-to-erbium is independent of the levels between which the transfer occurs.
Abstract: A study of the energy transfer process between thulium and erbium is presented. From our measurements of fluorescence emissions and decay times the energy transfer efficiencies and probabilities were calculated. In this work the energy transfer which occurs between the upper levels in the UV and VIS regions of the two ions was especially studied. In the Tm-Er system, a mutual migration of energy occurs. The energy transfer from thulium to erbium is a multichannel process in which the energy is transferred from all the metastable levels of thulium to the matching energy levels of erbium. In addition, backtransfer of energy from erbium to thulium occurs by crossrelaxation of respective erbium transitions. The efficiency of energy transfer from thulium to erbium is independent of the levels between which the transfer occurs, but is dependent on the matrix. It is concluded that the energy is transferred via the phonons of the host glass.


Journal ArticleDOI
TL;DR: In this paper, the attractive forces between the oncoming atoms and those deposited become important in determining the growth of the film when surface diffusion and many atom rearrangement processes are suppressed (precisely the conditions that lead to the formation of amorphous films).
Abstract: It is proposed that during the atom-by-atom deposition of a film, the attractive forces between the oncoming atoms and those deposited become important in determining the growth of the film when surface diffusion and many atom rearrangement processes are suppressed (precisely the conditions that lead to the formation of amorphous films). The trajectories of the oncoming atoms are distorted in such a way that the formation and growth of surface irregularities are favored. Since the deflection depends inversely upon the incident kinetic energy of the atoms, sputtered films should be smoother than evaporated films for equal substrate temperatures. It is also argued that this mechanism can lead to the formation of voids.

Journal ArticleDOI
TL;DR: In this paper, the role of glass phonons on the transition probabilities, halfwidth of emission bands and the Stokes shift is discussed, and the influence of the cavity and the site symmetry in which the rare earth is situated on transition probabilities is discussed.
Abstract: Oscillation strengths, emission and excitation spectra and decay times of Tm3+ and Er3+ in germanite glasses were measured. The results were compared with the data obtained previously in borate and phosphate glasses. The role of glass phonons on the transition probabilities, half-width of emission bands and the Stokes shift is discussed. Also, the influence of the cavity and the site symmetry in which the rare earth is situated on transition probabilities is discussed. Bands in the emission spectrum of Er3+, absent in the borate and phosphate, are detected in the germanite glasses. Probabilities of relaxation from 1 D 2 → 1 G 4 levels of Tm3+ in various glass hosts are calculated.