Showing papers in "Physica Status Solidi (a) in 1985"

Absorption Centers of Bi12GeO20 and Bi12SiO20 Crystals

Abstract: The energy gap of Bi12GeO20 (BGO) and Bi12SiO20 (BSO) crystals is about 3.2 eV. The yellow color of these crystals is due to a broad absorption shoulder in the photon energy range 2.3 eV < W < 3.2 eV, where the dependence of the absorption coefficient α ∼ (W – 2.3 eV)2 indicates an indirect optical transition. The variation of the optical absorption together with other physical properties such as lattice constant, mass density, photoconductivity, ultrasonic absorption, and melting temperature in different crystals and crystal regions indicate that BiGesi centers are responsible for the absorption shoulder rather than Ge/Si vacancies as was previously assumed. Die Bandlucke von Bi12GeO20 (BGO) und Bi12SiO20 (BSO)-Kristallen liegt bei 3,2 eV. Die gelbe Farbe beider Kristalle ruhrt von einer Absorptionsschulter im Photonenenergiebereich 2,3 eV < W < 3,2 eV her, wobei der Verlauf des Absorptionskoeffizienten α ∼ (W – 2,3 eV)2 einem indirelrten optischen Ubergang entspricht. Aus der Variation der optischen Absorption zusammen mit physikalischen Eigenschaften wie Gitterkonstante, Massendichtr, Fotoleitfahigkeit, Ultraschall- absorption, Schmelztemperatur in verschiedenen Kristallen und Kristallbereichen wird geschlossen, das fur diese Absorptionsschulter eher BiGe, si-Zentren verantwortlich sind als die bisher ange-nommenen Ge/Si-Leerstellen.

Pressure‐Induced Structural Transition in SrS

Abstract: SrS is studied by powder X-ray diffraction in the pressure range up to 350 kbar. A new phase transition is observed near 180 kbar, where SrS transforms from the rocksalt (B1) to the CsCl-type (B2) structure. The relative volume decrease is 11.4%. The transition is discussed in relation to systematic trends for B1B2 structural changes in other alkaline earth chalcogenides. Rontgenbeugungsmessungen an SrS werden im Druckbereich bis 350 kbar durchgefuhrt. Bei 180 kbar wird erstmals ein struktureller Phasenubergang beobachtet, bei dem sich SrS von der NaCl-Struktur (B1) in die CsCl-Struktur (B2) umwandelt. Die relative Volumenabnahme betragt 11,4%. Dieses Ergebnis wird im Zusammenhang mit der Systematik von B1B2-Ubergangen in anderen Erdalkalihalkogeniden diskutiert.

Electrical transport properties of In2Se3

Abstract: The electrical transport properties of In2Se3 are investigated. An attempt is made to elucidate the confusion concerning structure and polymorphism. Secondly measurements are made in high temperature range (α-β transition) and low temperature range on annealed and quenched samples. An unusual temperature dependence of the mobility is found that might be attributed to the defective structure of the stoichiometric vacancies in the cationic sublattice. The post-preparation annealing effect is also studied in detail and the difference is reported between an annealed and quenched-annealed sample. Les proprietes de transport electriques do In2Se3 ont ete etudiees. Tout d'abord, nous essayons d'elucider la confusion existant sur la structure et le polymorphisme du materiau. Puis nous decrivons les mesures effectuees ae hautes temperatures (region de la transition de phase α-β) et aux basses temperatures sur des echantillons trempes et recuits. La variation de la mobilite en fonction de la temperature n'est pas celle d'un semiconducteur classique; elle peut-ětre attribuee ae la structure lacunaire des sites cationiques et aux defauts de stoechiometrie. Nous avons aussi etudie en detail l'effet de recuit sur un echantillon trempe et l'avons compare avec un echantillon recuit lors de la preparation.

Irradiation-Induced Aggregate Centers in Single Crystal Al2O8

Abstract: Aggregate centers in reactor irradiated single crystal α-Al2O3 are investigated using the thermochemical and photochemical methods. Isochronal and isothermal annealings of the bands at 302, 356, 450, and 570 nm are performed in detail to study the thermal stability and to obtain the activation energy (E) for the decay of their corresponding centers. After X-ray irradiation at room temperature, a new band at 384 nm appears in the crystal irradiated previously by reactor radiation. From the thermochemical and photochemical properties as well as from correlations of these several bands, it is proposed tentatively that the 450 and 570 nm bands are attributed to the F type center, and the 302 nm band to the F2 center. Mittels thermochemischer und photochemischer Methoden werden Aggregatzentren in Reaktorbestrahlten α-Al2O3-Einkristallen untersucht. Isochrone und isotherme Temperungen der Banden bei 302, 356, 450 und 570 nm werden durchgefuhrt, um die thermische Stabilitat zu untersuchen und die Aktivierungsenergie (E) fur den Zerfall ihrer entsprechenden Zentren zu erhalten. Nach Bontgenbestrahlung bei Zimmertemperatur tritt eine neue Bande bei 384 nm in den vorher im Reaktor bestrahlten Kristallen auf. Aus den thermochemischen und photochemischen Eigenschaften sowie aus den Korrelationen dieser verschiedenen Banden wird vorlaufig angenommen, das die 450 und 570 nm-Banden dem F-Zentrum und die 302 nm-Bande dem F2-Zentrum zugeordnet sind.

Hydrogen Implantation into Silicon. Infra‐Red Absorption Spectra and Electrical Properties

Abstract: Hydrogen and deuterium implantations into crystalline silicon (c-Si) are carried out at room temperature. Infra-red spectra and electrical property studies are performed on these samples before and following annealing. Analysis of the vibrational spectra shows at least two types of bonding for hydrogen in c-Si, which are identified as SiH1, (SiH2)2 units. A strong evidence of SiH2 group formation is obtained for the relatively low hydrogen concentration in c-Si in comparison with a-Si:H. On the basis of the kinetics of formation and annealing of SiH vibrations and scanning micrograph data it is concluded that the microvoids with reconstructed inner surfaces, and hydrogen passivating dangling bonds, are effectively produced due to divacancy type defect agglomeration followed by hydrogen trapping. The electrical properties of c-Si:H are discussed also. [Russian Text Ignored].

Achievements in the field of physics and spectroscopy of activated laser crystals

Abstract: Professor Kaminskii started his two hour seminar by analyzing some peculiarities of cascade operating schemes of rare-earth activators on the base of stimulated emission excitation in multilevel ions at two contiguous lasing transitions. He considered the recent results of f-and d-activator ion investigations in the new laser crystal class with Cagallogermanate structure. He also discussed briefly the structural peculiarities and main luminescence and laser action characteristics of Nd3+ ions in La3Ga5SiO14, Nd3Ga5SiO14, La3Ga5GeO14, La3Ga5.5Nbg0.5O14, Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 single crystals. Finally, he discussed the data on luminescence and lasing parameters of Ca3Ga2Ge3O12 garnet with a new laser activator called “defect-center”.

The direct observation of discommensurations in barium sodium niobate (BSN) and its homologues

Abstract: Electron microscopic evidence is presented for the presence of discommensuration walls in incommensurate ferro-electric-ferro-elastic Ba2NaNb5O15 and its homologues Sr2KNb5O15 and Pb2KNb5O15. The displacement vector of the discommensuration walls is one fourth of a lattice vector of the orthorhombic commensurate superstructure, explaining the typical coalescence pattern of the discommensuration dislocations. The magnitude of the incommensurability is consistent with the density of discommensuration walls. Similarities and differences between the homologues are pointed out. Elektronenmikroskopische Hinweise fur die Anwesenheit von Diskommensurationswanden in inkommensurablem ferroelektrisch-ferroelastischem Ba2NaNb5O15 und seinen Homologen Sr2KNb5O15 und Pb2KNb5O15 werden gegeben. Der Verschiebungsvektor der Diskommensurations-wande betragt ein Viertel eines Gittervektors der rhombischen kommensurablen Superstruktur und erklart das typische Koaleszenzdiagramm der Diskommensurationsversetzungen. Die Grose der Inkommensurabilitat ist mit der Dichte der Diskommensurationswande konsistent. Ahnlichkeiten und Unterschiede zwischen den Homologen werden aufgezeigt.

The properties of crystals with garnet structure

Abstract: The results of investigations the elastic and photoelastic properties of a number of garnets crystals obtained by Mandelshtam-Brillouin technique including the data of ultrasonic experiments are represented. The velocity of sound propagation, the character of elastic interaction between ions in the lattice, nature of photon–phonon interaction in garnets is revealed. The mechanical, thermal and acoustooptical properties of garnets are rated using measured elastic and photoelastic data. The obtained results allow to predict a number of important characteristics of crystals with garnet structure and promote the development of materials with given properties. [Russian Text Ignored].

Monte‐Carlo simulation of keV‐electron scattering in solid targets

Abstract: By means of PWM-fitted screened Rutherford scattering, core ionization, and dielectric losses the scattering of electrons especially in Si-targets but also in Au, SiO2, and PMMA is investigated with regard to electron spectroscopy, electron probe microanalysis, and lithography. The behaviour of the electron backscattering fraction in its angular, energy, and depth distribution as well as the lateral escape density on the surface are obtained in dependence on the angle of incidence. Likewise the electron transmission and penetration with their spatial distributions and the resulting energy transfer to the target volume are illustrated. Mittels einer PWM-angepasten abgeschirmten Kutherford-Streuung, der Core-Ionisation und den dielektrischen Verlusten wird die Streuung von Elektronen speziell in Si-Targets, aber auch in Au, SiO2 und PMMA im Hinblick auf Elektronenspektroskopie, Elektronenstrahlmikroanalyse und Lithografie untersucht. Das Verhalten der Elektronenruckstreurate in ihrer Winkel-, Energie- und Tiefenverteilung, wie auch die laterale Austrittsdichte auf der Oberflache werden als Funktion des Einfallswinkels erhalten. Ebenso wird die Elektronentransmission und -penetration mit ihren raumlichen Verteilungen und der resultierende Energie transfer auf das Targetvolumen illustriert.

The morin transition in small α-Fe2O3 particles

Abstract: Magnetic properties of spherical hematite (α-Fe2O3) particles of narrow size distribution, having modal diameters ranging from 30 to 410 nm, are studied in the neighborhood of the Morin transition as a function of applied magnetic field with increasing and decreasing temperatures. It is found that this transition is of the first order and sensitive to the size of particles, their strain, and defects. An empirical result describing the influence of these contributions to the Morin temperature is obtained. The presented results strongly suggest that the magnetic “phases” proposed by Krupyanskii and Suzdalev do not exist. Die magnetischen Eigenschaften von kugelformigem Hamatit (α-Fe2O3)-Teilchen enger Verteilung (mit modalen Durchmessern zwischen 30 und 410 nm werden in der Nachbarschaft des Morin-Ubergangs in Abhangigkeit vom angelegten Magnetfeld bei steigenden und fallenden Temperaturen untersucht. Es wird gefunden, das dieser Ubergang von erster Ordnung ist und empfindlich gegenuber der Grose der Teilchen, ihrer Spannung und Defekte. Ein empirisches Ergebnis, das den Einflus dieser Beitrage zur Morintemperatur beschreibt, wird beobachtet. Das Ergebnis gibt einen starken Hinweis darauf, das die von Krupyanskii und Suzdalev vorgeschlagenen magnetischen „Phasen” nicht existieren.

Rate Dependence of the Field-Cooled Magnetisation of a Fine Particle System†

Abstract: A theory is developed of the field cooled magnetisation of a fine particle system. A cooling rate dependent „blocking temperature” is derived, by means of which the magnetisation of a system with a distribution of particle sizes can be calculated. Numerical calculations give good qualitative agreement with experimental results on cobalt aluminosilicate glasses. Eine Theorie fur die feldabgekuhlte Magnetisierung eines Kleinteilchensystems wird entwickelt. Eine „Sperrtemperatur” wird in Abhangigkeit von der Abkuhlrate berechnet und damit die resultierende Magnetisierung eines Systems mit Teilchengroseverteilung abgeschatzt. Numerische Berechnungen ergeben eine gute qualitative Ubereinstimmung mit Mesergebnissen an Kobaltaluminosilikatglasern.

Multicolor electroluminescent ZnS thin films doped with rare earth fluorides

Abstract: A systematic investigation of the electroluminescent (EL) ZnS thin film devices doped with rare earth centers, SmF3 (red), TbF3 (green), and TmF3 (blue), is made to examine the possibility of multicoloring. Various characteristics, such as brightness, emission efficiency, decay time, EL spectra, and their concentration dependences are measured. The number of photons emitted from these devices is also estimated to discuss quantum efficiencies. For SmF3 and TmF3 activators, it is found that concentration quenching of EL emission takes place through non-radiative crossrelaxation process. No such quenching is observed for TbF3 activators. In TmF3 activators, most of the radiative energy is found to be emitted in the infrared region. The impact excitation cross-section for these rare earth compounds is also inferred to be lower compared with that of Mn2+ ions.

Infra-Red Spectra, Electron Spin Resonance Spectra, and Density of (TeO2)100-x-(WO3)x and (TeO2)100-x-(ZnCl2)x Glasses

Abstract: Two series belonging to the systems (TeO2)100−x–(WO3)x and (TeO2)100−x–(ZnCl2)x [0 ≦ x ≦ 33.8%] are prepared in the glassy state. The infra-red spectra of the two series are studied in the range 200 to 4000 cm−1. The main IR absorption bands in both series are related to the characteristics of TeO2. The detected shift in these bands are found to be sensitive to the glass structure. The electron spin resonance of the system (TeO2)100−x–(WO3)x is recorded. It is found that the ratio of (W5+/W6+) increases with the increase of WO3 content. The composition dependence of the density shows an increase as the WO3 content increases and a decrease as the ZnCl2 content increases. Zwei Serien, die zu den Systemen (TeO2)100−x–(WO3)x und (TeO2)100−x–(ZnCl2)x [0 ≦ x ≦ 33.8%] gehoren, werden im Glaszustand prapariert. Die Infrarotspektren der beiden Serien werden im Bereich 200 bis 4000 cm−1 untersucht. Die starksten IR-Absorptionsbanden in beiden Serien werden mit den Charakteristiken von TeO2 verknupft. Die beobachtete Verschiebung in beiden Banden ist sensitiv gegenuber der Glasstruktur. Die Elektronenspinresonanz des Systems (TeO2)100−x–(WO3)x wird aufgezeichnet. Es wird gefunden, das das Verhaltnis von (W5+/W6+) mit dem WO3-Gehalt zunimmt. Die Zusammensetzungsabhangigkeit der Dichte zeigt einen Anstieg, wenn der WO3-Gehalt zunimmt und eine Abnahme, wenn der ZnCl2-Gehalt zunimmt.

Ruby structure peculiarities derived from X‐ray diffraction data localization of chromium atoms and electron deformation density

Abstract: An accurate, X-ray diffraction study is made of the atomic and electronic structure of the ruby crystal Al2O3:Cr3+. Least-squares high-angle refinement (R = 0.0069, Rw = 0.0099, S = 1.055) for 180 independent reflections shows that the Cr-atoms substitute the Al-atoms not precisely at the sites of the latter, but are shifted along the c-axis at a distance of 0.13 A towards the vacant octahedral holes; this is in agreement with some previous spectral data. In the electron deformation density map this displacement manifests itself as a peak 0.30 A−3 which is absent in the pure rorundum crystal. The deformation electron density and the electrostatic potential distribution in cuby crystal are analyzed in detail. Es wird eine genaue Rontgenbeugungsuntersuchung der atomaren und elektronischen Struktur des Rubinkristalls Al2O3:Cr3+ durchgefuhrt. Eine Winkelbestimmung nach der Methode der kleinsten Quadrate (R = 0,0069, Rw = 0,0099, S = 1,055) fur 180 unabhangige Reflexe zeigt, das die Cr-Atome die Al-Atome nicht prazise auf deren Platze substituieren, sondern auf der c-Achse um die Distanz 0,13 A in Richtung der unbesetzten Oktaederlucken verschoben sind in Ubereinstimmung mit einigen fruheren Spektralwerten. Im Diagramm der Elektronendichtedeformation zeigt sich diese Verschiebung als ein Maximum 0,30 A−3, das im reinen Korundkristall fehlt. Die Elektronendichtedeformation und Potentialverteilung im Rubinkristall wird ausfuhrlich analysiert.

The Effect of Temperature on Dislocation Structures in Ni3Al

Abstract: The deformation structures present in polycrystalline Ni3Al after tensile testing at temperatures from 77 to 1023 K are examined using transmission electron microscopy. Dislocations are present as APB-pairs. In addition, at low temperatures S–ISF pairs are common, usually in the form of truncated elongated loops. A transition from {111} to {100} slip around the temperature of the peak yield stress is found, in agreement with the observations of earlier workers on other Ll2 alloys. Dislocations are usually straight at low strains but can be bowed at higher strains. At high temperatures rows of perfect loops are common and dynamic recrystallization occurs. Mit Hilfe der Elektronenmikroskopie werden die Verformungsstrukturen untersucht, die in polykristallinem Ni3Al im Temperaturbereich von 77 bis 1023 K vorhanden sind. Verlagerungen sind als APB-Paare vorhanden. Zusatzlich treten haufig bei niedrigen Temperaturen S–ISF-Paare auf, gewohnlich in der Form von abgeflachten langlichen Schleifen. Im Bereich der Temperatur der maximalen Elastizitatsspannung wird ein Ubergang von der {111}- auf {100}-Gleitung gefunden; dies stimmt mit den Beobachtungen anderer Autoren an Ll2 Legierungen uberein. Die Verlagerungen sind gewohnlich unter niedrigen Spannungen gerade ausgerichtet, konnen aber bei hoheren Belastungen gebogen oder gekrummt sein. Bei hoheren Temperaturen sind Reihen von perfekten Schleifen haufig und eine dynamische Rekristallisation tritt auf.

Diffusion of chromium in α‐iron

Abstract: In the temperature range from 915 to 1124 K interdiffusion coefficients in b.c.c. iron-chromium alloys are determined for concentrations up to 28 at% Cr. Above the Curie temperature of pure iron the concentration dependence of the interdiffusion coefficients shows a maximum at 13 at% Cr correlated with the minimum of the solidus line. For lower temperatures the magnetic ordering shifts the maximum to higher concentrations. The transition to magnetic long range order is marked by a discontinuity in the concentration gradient. The temperature minimum in the γ loop is found between 1124 and 1129 K.

Deformation mechanisms and the theory of structural superplasticity of metals

Abstract: A new model of structural superplasticity is proposed on the basis of recent experimental data on the operative deformation mechanisms and the results of investigations of grain boundary properties. The concepts of hardening and recovery are used to analyse the superplastic nature, the development of these processes being associated with grain boundaries. According to the proposed model during superplastic flow the hardening due to easy generation of lattice dislocations (LD's) in the boundaries at the formation of grain boundary dislocation pile-ups is insignificant while the rate of the recovery whose kinetics is determined by LD absorption by boundaries is high. On the basis of these conceptions a system of equations of the dislocation kinetics is obtained which describes the experimental curve of superplastic deformation and the principal causes of a number of structural effects which have not been satisfactorily explained before are given. [Russian Text Ignored].

Investigations of Hydrogen Implanted GaP Single Crystals by Means of Particle Induced γ‐Spectroseopy, Infrared Spectroscopy, and Rutherford Backscattering Channelling Technique

Abstract: The incorporation of hydrogen into GaP single crystals bombarded with 0.3 and 1.0 MeV protons it investigated in the fluence range to 1018 cm−2. The combination of infrared spectroscopy and trarticle induced γ-spectroscopy with the Rutherford backscattering channelling technique enables to study hydrogen incorporation, hydrogen trapping, and lattice damage and to determine the satio of the chemically bonded to the total incorporated amount of hydrogen dependent on the defect profile. The use of the ion beam etching technique allows the investigation of depth profiles within larger depth regions. Die Einlagerung von Wasserstoff in mit 0,3- und 1,0 MeV-Protonen beschossenen GaP-Einkristallen wird im Dosisbereich bis 1018 cm−2 untersucht. Durch die Kombination von Infrarotspek-troskopie und teilcheninduzierter γ-Spektroskopie mit der Rutherford-Ruckstreu-Kanalisierungs-technik gelingt es, Aussagen zu treffen uber die Wasserstoffeinlagerung, die Wasserstoffanlagerung, die Strahlenschadigung und das Verhaltnis von chemisch gebunden zu ungebunden enthaltenem Wasserstoff. Der Einsatz der Schragschlifftechnik gestattet die Aufnahme von Wasserstoffkonzentrationsprofilen bis in grosere Tiefenbereiche.

Optical Properties of the Two Crystal Modifications of the Organic Conductor (BEDT-TTF)2I3

Abstract: Polarised reflectivity spectra in the region 200 to 30000 cm−1 are investigated for the two crystal modifications of (BEDT-TTF)2I3: the dielectric α-phase and the superconducting β-phase. For both phases the electronic reflection bands with a Drude-like edge are observed in two perpendicular polarisations at room temperature, for the α-phase the most intense electronic band being observed in the direction perpendicular to BEDT-TTF stacks. In the IR spectra of both phases the bands due to the interaction of molecular vibrations with conduction electrons are observed. For the α-phase the IR reflection spectra at temperatures above and below the dielectric transition points are obtained and an increasing number of bands in the vibrational region is found below the transition point. [Russian Text Ignored].

X-Ray study of the thermal expansion anisotropy in AgGaS2 and AgInS2 compounds over the temperature range from 80 to 650 K

Abstract: The lattice parameters α and c of the AgGaS2 and AgInS2 compounds are determined as a function of temperature by X-ray diffraction method in the temperature range from 80 to 650 K. The data are used to evaluate the coefficients of thermal expansion, perpendicular (α⟂) and parallel (α∥) to the principal axis, and the thermal expansion of the AC (αAC) and BC (αBC) bonds. It is found that for the two compounds almost over the whole investigated temperature range the coefficients of expansion α∥ and αBC are negative while the coefficients α⟂ and αAC are positive. [Russian Text Ignored].

Hole‐induced exoelectron emission and luminescence of corundum doped with Mg

Abstract: Thermally stimulated exoelectron emission (TSEE) and thermally stimulated luminescence (TSL) preliminary excited by X-rays of Al2O3 single crystals containing different amounts of Mg impurities and treated under oxiding and reducing conditions are investigated. TSEE and TSL are found to be due to the recombination process of holes thermally released from traps on Mg2+ ions (TSEE and TSL peaks at 230 K) as well as of electrons thermally released from traps (TSEE and TSL peaks at 255 K). TSEE is observed synchronously with the F-centre emission in the 3.0 eV band both, in the hole and electron recombination process. The experimental results are interpreted basing on the model of hole-electron recombination in the two-centre Auger-process. [Russian Text Ignored].

Conductivity Instabilities and Polarization Effects of Bi12(Ge, Si) O20 single-Crystal Samples

Abstract: When subjected to measurements of temperature-dependent dark conductivity and thermally stimulated currents, undoped and lightly doped Bi12GeO20 (BGO) and Bi12SiO20 (BSO) crystal samples often show a very strange shape and hysteresis behaviour of their photocurrent response characteristics as well as marked instabilities. Taking into account the positive space charge layer at the cathode, which is deduced from depolarization currents and electrooptical observations, these instabilities can be attributed to negative space charge currents of electrons injected at some points on the cathode, spreading out in cone-like paths to the anode. AC measurements reduce these instabilities. Measured values for the dark current activation energy are (1.1 ± 0.07) eV and 10−10 to 5 × 10−2 cm2/Vs for the photocarrier drift mobility, increasing with illumination.

Phase transitions between the quasicrystalline, crystalline, and amorphous phases in Al16 at% V

Abstract: By means of electron irradiation the amorphous state can be produced in quasicrystalline and crystalline Al14 at% Mn. The transitions between these three phases are studied in situ in a high-voltage electron microscope. The behaviour of the quasicrystalline phase exhibits features distinctly different from those of the crystalline phase. Under certain conditions the phase transition quasicrystalline–amorphous is reversible and the quasicrystalline phase develops from the amorphous state. From the temperature dependence of the transformation kinetics conclusions can be drawn on the temperature dependence of atom transport in the phases investigated. Mit Hilfe von Elektronenbestrahlung last sich in quasikristallinem und kristallinem Al14 at% Mn der amorphe Zustand einstellen. Die Ubergange zwischen diesen drei Phasen werden in situ in einem Hochspannungselektronenmikroskop untersucht. Die quasikristalline Phase zeigt dabei ein Verhalten, das deutlich verschieden ist von dem der kristallinen Phase. Der Ubergang quasi-kristallin–amorph kann reversibel gefuhrt werden, d. h. unter bestimmten Bedingungen bildet sich aus dem amorphen wieder der quasikristalline Zustand. Aus der Temperaturabhangigkeit der Kinetik der Phasenubergange last sich auf die Temperaturabhangigkeit des Atomtransportes in den untersuchten Phasen schliesen.

Cation distribution in MgxNi1−xGa2O4 oxide spinels

Abstract: Spinels MgxNi1–xGa2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) are synthesized, in polyerystalline form, by solid-state reaction at 1273 K of the individual metal oxides. X-ray diffraction is used to determine the lattice parameter (a0), cation distribution, and oxygen parameter (u) for each spinel. Complete solid solution formation between MgGa2O4 and NiGa2O4 is found, and a0 increases linearly with the composition parameter, x; the oxygen parameter, however, remains approximately constant at u = 0.382 (±1). The cation distribution is found to be dependent upon chemical composition, the proportion of octahedral Ni2+ increasing as the amount of Mg2+ is raised. These results are interpreted in terms of the interplay of the different factors which determine the crystal chemistry of metal oxides. Au moyen d'une reaction a l'etat solide (1273 K) dans les oxydes metalliques individuels, on a synthetise la serie de spinelles MgxNi1–xGa2O4 (x = 0; 0,2; 0,4; 0,6; 0,8; 1) et l'on a determine, moyennant diffraction de rayons X, le parametre de maille (a0), la distribution de cations et le parametre de l'anion (u) correspondant a chaque spinelle. On a trouve que les composes MgGa2O4 et NiGa2O4 forment une serie de solutions solides ou a0 augmente de facon lineaire a mesure que le parametre de composition, x, augmente. Le parametre de l'anion, par le contraire, garde la valeur pratiquement constante u = 0,382 (±1). Il se trouve que la distribution des cations est dependante de la composition chimique, car la proportion de Ni2+ hexacoordonne augmente a mesure que l'on augmente le contenu de Mg2+ des spinelles. Ces resultats sont interpretes en termes de l'interrelation qui existe parmi les differents facteurs qui determinent la structure cristalline des oxydes metalliques.

Influence of organic molecules on the current-voltage characteristic of planar MIM diodes

Abstract: Electroformed planar metal-insulator-metal (MIM) diodes are treated in various organic gas environments exhibiting characteristic influences on their current-voltage behaviours. Certain groups of molecules cause (i) differently strong increases of the conductivity (starting from the OFF state), (ii) ceasing the VCNR shapes (ON state), or (iii) no changes. Qualitatively is shown that the VCNR behaviour corresponds to organic molecule fragments in the mass spectra. Elektroformierte, planare Metall-Isolator-Metall (MIM)-Dioden zeigen bei Behandlung mit zahl-reichen organischen Gasen charakteristische Veranderungen im Strom-Spannungs-Verhalten. Bestimmte Molekul-Gruppen verursachen (i) ein unterschiedlich starkes Anwachsen der Leit-fahigkeit (ausgehend vom OFF-Zustand), (ii) ein Verschwinden des Maximums (VCNR-Verlauf, ON-Zustand) oder (iii) keine Veranderungen. Qualitativ wird gezeigt, das das VCNR-Verhalten mit organischen Molekulfragmenten im Massenspektrum korrespondiert.