Showing papers on "Lattice constant published in 1982"

Material parameters of In1−xGaxAsyP1−y and related binaries

Abstract: Various models for calculation of physical parameters in compound alloys are discussed and the results for In1−x Gax Asy P1−y quaternaries are presented. The model used is based on a linear interpolation scheme, and therefore necessitates known values of the parameters for the related binary and ternary alloys. The material parameters considered in the present study can be classified into the following eleven groups: (1) lattice constant and crystal density, (2) thermal expansion coefficient, (3) electronic‐band structure, (4) external perturbation effect on the lowest‐direct gap, (5) effective mass, (6) dielectric constant, (7) Frohlich coupling parameter, (8) elastic properties, (9) piezoelectric properties, (10) deformation potential, and (11) excitonic effect. Of particular interest is the deviation of material parameters from linearity with respect to the alloy composition. It is found that the present model provides generally acceptable parameters, in good agreement with the existing experimental da...

Electrical properties and defect model of tin-doped indium oxide layers

Abstract: Tin-doped In2O3 layers were prepared by the spray technique with doping concentrationsc Sn between 1 and 20 at. % and annealed at 500 °C in gas atmospheres of varying oxygen partial pressures. The room-temperature electrical properties were measured. Maximum carrier concentrationsN=1.5×1021cm−3 and minimum resistivities ϱ=1.3×10−4 Ω cm are obtained if the layers are doped withc Sn≈9 at. % and annealed in an atmosphere of oxygen partial pressurep O2 ⋦10−20 bar. At fixed doping concentration, the carrier mobility increases with decreasing oxygen pressure. The maximum obtainable mobility can be described in terms of electron scattering by ionized impurities. From an analysis of the carrier concentration and additional precision measurements of the lattice constants and film thicknesses, a defect model for In2O3:Sn is developed. This comprises two kinds of interstitial oxygen, one of which is loosely bound to tin, the other forming a strongly bound Sn2O4 complex. At low doping concentrationc Sn≲4 at. % the carrier concentration is governed by the loosely bound tin-oxygen defects which decompose if the oxygen partial pressure is low. The carrier concentration follows from a relationN=K 1 ·p O2 −1/8 ·(3 ×1010 × cSn −N)1/4 with an equilibrium constantK 1=1.4×1015 cm−9/4bar1/8, determined from our measurements.

Properties of AlxGa1−xN films prepared by reactive molecular beam epitaxy

Abstract: Single‐crystal films of the solid solution AlxGa1−xN of the entire composition range have been fabricated on sapphire and silicon substrates by reactive molecular beam epitaxy (MBE) at 700 °C. The properties of the films have been studied by the reflection high energy electron diffraction technique, x‐ray diffraction, and electrical and optical measurements. The lattice constant of the film is not a linear function of the composition, and the fundamental absorption edge also shows nonlinear dependence on the composition. The narrow intense peak of the cathodoluminescence concerned with the band to band or shallow impurity band transition, varies from 3.4 to 6 eV with the composition, which suggests the feasibility of AlxGa1−xN films grown by reactive MBE for optical devices in the ultraviolet spectral region.

X-ray study of phase transitions in efrroelectric Na0.5Bi0.5TiO3

Abstract: The temperature dependence of the lattice constant in Na0.5Bi0.5TiO3 single crystal was studied by means of X-ray diffraction. Two structural phase transitions were found in the temperature range 293-920 K: the cubic-to-tetragonal at 793 ± 5 K and the tetragonal-to-rhombohedral at 533 ± 5 K. The dielectric permittivity was measured and a considerable dispersion was observed. The shift of the dielectric permittivity maximums are linear in coordinates 1/T = F(In f).

Pseudopotentials and Total Energy Calculations

Abstract: It has recently become possible to use pseudopotential and total energy techniques to determine crystal structures, solid-solid phase transformations, lattice constants, bulk moduli, shear moduli, cohesive energies, phonon spectra and other static and dynamical properties of solids. The only inputs are the atomic number and mass of the constituent elements and a group of crystal structures to test, yet the results are highly accurate. Some of these results together with a description of the development of the pseudopotential approach and applications are presented.

A Computer Program for Refinement of Crystal Orientation Matrix and Lattice Constants from Diffractometer Data with Lattice Symmetry Constraints

Abstract: A linear least-squares computer program that implements the procedure described by Shoemaker & Bassi [Acta Cryst. (1970), A26, 97–101] has been written. With this technique constraints appropriate to the lattice symmetry may be imposed during refinement of the coefficients of the orientation matrix. Cell parameters and variances with the assumed lattice symmetry and the best least-squares agreement result from this calculation.

The lattice parameter of highly pure silicon single crystals

Abstract: From crystal to crystal comparison, thed220 lattice spacing in PERFX and WASO silicon crystals used in the only two existing absolute measurements have been found to be equal within ±2×10−7d220. This demonstrates that generic variabilities of the two crystals account only for a small part of the 1.8×10−6d220 difference in the two absolute measurements. In a new series of 336 single measurements, ourd220 value reported recently has been confirmed within ±2×10−8d220. From these results we derive the following lattice parameter for highly pure silicon single crystals:a0=(543 102.018±0.034) fm (at 22.5°C, in vacuum).

Solid Solubility of Aluminum and Boron in Silicon Carbide

Abstract: Solid solubility of aluminum in silicon carbide was studied by the powder X-ray diffraction technique (Debye-Scherrer method). At 2200° C the solubility limit was 1.0 wt%. Measurements of the lattice parameter of Al-saturated samples as a function of temperature gave a heat of solution of 147 kJ/mol. The change in the lattice parameter indicates that Al substitutes for Si. Literature data are interpreted as indicating that B replaces both Si and C.

Total-energy calculations for Si with a first-principles linear-combination-of-atomic-orbitals method

Abstract: The total energy for Si with various lattice distortions has been calculated using a first-principles linear-combination-of-atomic-orbitals method. The physical properties derived from these calculations include not only the equilibrium lattice constant, cohesive energy, and bulk modulus, but also the internal strain parameter and several phonon frequencies including anharmonic terms. For all these properties there is good agreement with experiment. The frozen-core approximation was tested and found to be valid for Si in a large region about the equilibrium lattice position.

Curie temperature and lattice constant of oxidized titanomagnetite and grain size effect on the low-temperature

Abstract: Summary. Low-temperature oxidation of titanomagnetites (x = 0.3, 0.5 and 0.7) was investigated in this study. Starting materials were carefully prepared so that their Curie points and lattice constants were in agreement with reliable values. Changes in Curie points and lattice constants during the process of low-temperature oxidation were then studied in detail. Independent heatings were performed under various conditions and oxidation parameters (z) were determined by chemjcal analyses. Though this method could not provide continuous z values like the weight increase method, reproducibility was very high when samples were heated in the same condition and the various states were consistent with each other. Oxidation states from z = 0.0 to 1.0 were realized in three compositions. When titanomagnetite in basalt was heated under various conditions a change occurred, either oxidation, decomposition or reduction. Natural titanomagnetite minerals closely followed the oxidation-reduction trends established for synthetic samples. The present results are consistent with those of Readman & O’Reilly with some exceptions. The differences may have been caused by the differences in starting materials. The results of Keefer & Shive are similar to those of Ozima & Sakamoto and are completely different from ours. They detected a rhombohedral phase and indicated that the decomposition process proceeds in the same manner reported by Ozima & Sakamoto. We are unable to account for their results. It may be useful to consider the results of Ozima & Sakamoto as a decomposition process. This idea has not been presented previously in the literature.

Manufacture of semiconductor device

Abstract: PURPOSE:To restore a crystal defect by ion implantation at a heat-treatment temperature by a method wherein, in a heat-treatment method used to restore the crystal defect by implanting impurity ions into a compound semiconductor provided with a heterostructure, a composition ratio of elements constituting a first semiconductor layer is set to a value by which a lattice constant of the first semiconductor layer nearly coincides with a lattice constant of a second semiconductor layer. CONSTITUTION:An n-InP buffer layer 2, an n InGaAs light-absorbing layer 3, an n InGaAsP intermediate layer 4, an n InP multiplication layer 5 and an InGaAsP cap layer 6 are formed one after another on an n InP substrate 1 by using a liquid phase epitaxy method. During this process, a composition ratio of the InGaAsP intermediate layer 4 is set to a value which is lattice- matched to InP near a heat-treatment temperature (about 790 deg.C) at a posterior process, e.g. In0.716Ga0.284As0.613P0.387. When it is lattice-matched at the heat- treatment temperature in this manner, a strain at a heterointerface between the intermediate layer 4 and the multiplication layer 5 is eliminated; accordingly, a crystal defect by ion implantation can be restored sufficiently.

Relation between Structural and Magnetic Properties of Compound MnAs1-xPx (0≦x≦0.275)

Abstract: The crystallographic parameters of compounds MnAs 1- x P x (0≦ x ≦0.275) are determined as a function of temperature between about 100 and 600 K. It is found that these crystals except for MnAs take a MnP type structure in low temperature side and transform to a NiAs type at critical temperatures. These structural transitions are of second kind and accompanied with very large dilation (∼10%) of crystal volume. In order to see the relationship between the structural and magnetic properties, the temperature variation of magnetic susceptibilities of the compounds is also measured. Simple analysis of the experimental results, based on the Curie-Weiss law, reveals the way in which the spin value of Mn atoms and the exchange interaction between them depend on the crystal voluem (or lattice parameter).

New Type of A 5 B 3 Structure in Al-Ti and Ga-Ti Systems; Al 5 Ti 3 and Ga 5 Ti 3

Abstract: By electron diffraction and X-ray powder diffraction, a new type of A5B3-structure based on the L10-type was found in the Al–Ti and Ga–Ti systems; Al5Ti3 and Ga5Ti3. The structure has a tetragonal symmetry with the space group, P4/mbm, and the lattice constants, 2√2af and cf, where af and cf are those of the fundamental L10-type cell. 20 Al (or Ga) and 12 Ti atoms are contained in the unit cell. The structure can be described as follows: it consists of the domains based on the L12, containing 3×2 columns of Ti atoms, and the domain boundaries have the L10-type atomic arrangement.

The structure of dinitrogen tetroxide N2O4: Neutron diffraction study at 100, 60, and 20 K and ab initio theoretical calculations

Abstract: Single crystal neutron diffraction studies are reported for cubic dinitrogen tetroxide (space group Im3; Z = 6). The crystals were grown from NO2 vapor in situ on the diffractometer by precise cryostatic control. The lattice parameter, measured at seven temperatures, increases from 7.6937(6) A at 20 K to 7.7925(6) A at 140 K. The nuclear positional and thermal parameters were refined using diffraction data (sin ϑ/λ⩽0.79 A−1) measured at 20, 60, and 100 K. Final fit indices R(F2) are 0.028, 0.034, 0.037, respectively. The observed N–N bond length and O–N–O angle are invariant between 20 and 100 K at values 1.7562(±4) A and 134.46(±6)° with individual e.s.d.’s of 0.001 A and 0.1°. The observed N–O bond length increases linearly from 1.1855(9) A at 100 K to 1.1893(5) A at 20 K; the extrapolated zero‐point value is 1.191 A. Ab initio self‐consistent field calculations using a two‐configuration wave function which allows partial occupation of the σ* MO (antibonding with respect to the two nitrogens) yields a r...

Valence state of cerium in the hexagonal CeM5 compounds with the transition metals

Abstract: 2014 The valence state of cerium in CeCo5, CeNi5, CeCu5 and the pseudo-binary Ce(Ni1-xCux)5 compounds has been studied by means of measurements of lattice parameters, magnetic properties and X-ray absorption. Whereas the lattice parameters of CeCu5 correspond to a Ce3+ valence state, X-ray absorption experiments show that, in CeCo5 and CeNi5, Ce has the same valence state, close to 4 +, as in the insulator CeO2. Stoichiometry deviations in the RCo5 compounds (R = rare earth) can be correlated with the difference in the anomalies of the 03B1 lattice parameter of Ce compounds in the RCo5 and RNi5 series. In Ce(Ni0.1Cu0.9)5, Ce is in the 3+ state and the thermal variation of the susceptibility is characteristic of crystal field effects in the Ce3+ ion. In contrast the susceptibility of CeNi5 is one order of magnitude smaller and almost isotropic; as in YNi5, it arises mainly from the Ni 3d electrons which are close to the onset of ferromagnetism. In the Ce(Ni1-xCux)5 compounds, the Ce valence state decreases linearly with x up to x = 0.3 and more rapidly for higher copper concentrations. The evolution of the Ce valence state is discussed in terms of the band structure of the different compounds, especially the relative position of the Fermi level and the 4f1 state. J. Physique 43 (1982) 173-180 JANVIER 1982,

Thermal expansion, Gruneisen functions and static lattice properties of quartz

Abstract: Reports measurements of the thermal expansion of quartz both parallel and perpendicular to the trigonal axis, at temperatures between 17 and 30K, between 575 and 85K, and a 283K These measurements confirm the qualitative inadequacy of the SiO4 tetrahedral tilt model Together with other thermodynamic data, the results are used to derive Gruneisen functions gamma perpendicular to (T) and gamma /sub ///(T) for temperatures up to 923K gamma perpendicular to (T), gamma /sub ///(T) and the heat capacity are analysed to give the moments ( omega n) of the vibrational frequency distribution, the equivalent Debye temperature theta D(n) and the Gruneisen functions gamma perpendicular to (n) and gamma /sub ///(n) These can be used to estimate various crystal properties For the equilibrium static lattice, the energy and lattice constants are respectively: EL=-1876+or-5 kJ mol-1; aL=4875+or-0005 AA; cL=5380+or-0005 AA The temperature variation of the Gruneisen functions is discussed in the light of available spectroscopic data, and the positive expansion of alpha -quartz is attributed to high values of normal mode Gruneisen parameters in the upper parts of the acoustic branches and in some of the lower optical branches

Electronic structure of GaAsxP1−x/GaP strained‐layer superlattices with x<0.5

Abstract: The electronic properties of GaAsxP1−x/GaP(100) strained‐layer superlattices with x<0.5 are studied using both a tight‐binding model and an effective‐mass model. By varying the alloy compositions and thicknesses of the layers, it is possible to independently vary the band gap and lattice constant of these structures. For the structures in which the bulk [100] minima are mapped into the strained‐layer superlattice Γ point, a direct band gap occurs in the superlattice even though the bulk materials have indirect gaps. The results illustrate that strained‐layer superlattices in general form a broad new class of semiconductor materials with tailorable electronic properties.

Effect of hydrogen absorption on the magnetic properties of ZrMn2−xFex ternaries with a C14 structure

Abstract: Magnetization measurements were carried out on ZrMn 2− x Fe x ( x = 0.4, 0.7 and 1.0) and their hydrides. All systems possess a hexagonal Laves phase structure (C14 structure). These compounds are found to absorb about 3.6 hydrogen atoms per formula unit. The hydrogen absorption is accompanied by a large expansion in volume ranging from 26% to 28% with no change in crystal structure. In this system, both the magnetic moments and the transition temperatures were found to be significantly larger in the hydride phases than in the corresponding host compounds. An increase in the magnetic moments on hydrogenation can be interpreted as a result of charge transfer from the transition metal atoms to hydrogen due to the difference of electronegativity. An increase in the magnetic ordering temperatures is attributed to a decrease in the electron concentration of 3d bands as well as to an increase in the lattice constants on hydrogenation. Spin glass behavior is exhibited by all the systems studied. The spin glass behavior is thought to originate from iron-rich clusters which occur as a consequence of statistical fluctuations in the manganese sublattice.

Magnetic excitations and lattice vibrations in uranium rock-salt structure compounds

Abstract: The inelastic magnetic and lattice vibrational scattering of neutrons from several uranium pnictides (UN, UAs, and USb) and chalcogenides (US, UTe) have been measured in recent years. The character of the low‐temperature magnetic scattering depends on the lattice constant. The compounds with the largest lattice parameters (USb, UTe) exhibit several branches of well defined magnetic excitations. The other compounds exhibit only a broad, featureless frequency response at low temperature, which may be extremely weak, as in new data presented here for US. Nonetheless, intense paramagnetic scattering is observed above the ordering temperature, with a marked 2d anisotropy in all the pnictides. A force‐constant analysis of the phonon dispersion relations for these materials has been carried out. We show here that UTe, US, and UAs have negative values of the elastic constant C12, as has been found in certain mixed valence compounds. As expected from the increase in ionic size, the compressibility increases with t...