Showing papers on "Lattice constant published in 1975"
IBM1
TL;DR: In this article, Kohn and Sham showed that the cohesive energy, lattice constant, and bulk modulus of Li, Be, Na, Al, Ar, K, Ca, and Cu can be computed using the local density scheme of Kohn, to within \ensuremath{\sim}20% and \ensuresuremath{sim}03 Bohr radii, and ≤ 1.10% respectively, of experimental values.
Abstract: We show that the cohesive energy, lattice constant, and bulk modulus of Li, Be, Na, Al, Ar, K, Ca, and Cu can be calculated using the local-density scheme of Kohn and Sham, to within \ensuremath{\sim}20%, \ensuremath{\sim}03 Bohr radii, and \ensuremath{\sim}10%, respectively, of experimental values These calculations are truly a priori in that the only inputs are the atomic number $Z$ and the zero-point lattice properties Self-consistent crystal calculations were performed using the muffin-tin approximation, and atomic calculations were performed using the spin-polarized exchange-correlation functional constructed by von Barth and Hedin The results show that these approximations are adequate for computing the equilibrium properties of crystals (errors in the computed pressure-volume relations are less than \ensuremath{\sim} 10 kbar), but errors occur in the atomic calculations for atoms with more than one electron outside a closed shell, and possibly in the muffin-tin approximation for transition-element crystals
272 citations
TL;DR: A silicon powder standard reference material, SRM-640, has been prepared for use as a standard in powder diffractometry as discussed by the authors, which can be used to obtain accurate measurements of lattice parameters.
Abstract: A silicon powder Standard Reference Material, SRM-640, has been prepared for use as a standard in powder diffractometry. Powder diffraction measurements were performed with a tungsten internal standard and a high-angle goniometer. The measured a/λ is 3.525176. With λ(Cu Kα1 peak) taken as 1.5405981 A, a = 5.430880 (35) A, uncorrected for refraction. Comparison of a with values obtained with a single-crystal from one of the boules reveals a difference of 3 parts in 105. This difference suggests a subtle systematic error in powder diffractometry or a change in lattice spacing near crystal boundaries. Use of the SRM should permit individual measurements of lattice parameters to be made reproducible to near 1 part in 105 and an absolute accuracy of at least 3 parts in 105.
148 citations
TL;DR: The lattice constants of a diamond platelet and of large single, undoped, crystals of silicon and germanium have been determined from measurements of multiple diffraction patterns by the method described in Part I as discussed by the authors.
Abstract: The lattice constants of a diamond platelet and of large single, undoped, crystals of silicon and germanium have been determined from measurements of multiple diffraction patterns by the method described in Part I [Post (1975). J. Appl. Cryst. 8, 452–456]. The mean values, based on measurements of eight to twelve reflections, and their standard deviations are: diamond a = 3.566986 A, Aa/a = 2.6 × 10−6; silicon a = 5.430941 A, Aa/a = 2 × 10−6; germanium a = 5.657820 A, Δa/a = 1.6 × 10−6.
133 citations
TL;DR: In this paper, contamination-free TiNx was prepared and the lattice parameter (a0) -nitrogen content (x) relation determined and the result can be expressed as a0 = 4.1925 + 0.0467x (in A) in the range 0.605 ≤ x ≤ 0.999.
Abstract: Contamination-free TiNx was prepared and the lattice parameter (a0)–nitrogen content (x) relation determined. The result can be expressed as a0 = 4.1925 + 0.0467x (in A) in the range 0.605 ≤ x ≤ 0.999. Density measurement showed that no titanium vacancies existed in the lattice.
96 citations
TL;DR: In this article, the authors investigated the effect of controlled vapour pressure on the generation of rooty faults and showed that the lattice constant of the epitaxially grown GaP and GaAs under controlled CVP has a minimum value at optimum pressure.
92 citations
TL;DR: In this paper, the authors studied the effect of fast neutron irradiation on gallium arsenide and showed that the electrical resistivity increases with dose at low doses to semi-insulating values, showing a remarkable, specimen-independent decrease for doses greater than 1017 n cm-2.
Abstract: The damage produced by fast neutron irradiation of gallium arsenide has been studied by a number of techniques. The electrical resistivity, which increases with dose at low doses to semi-insulating values, shows a remarkable, specimen-independent decrease for doses greater than 1017 n cm-2 from values of ca. 109 Ω cm to 3 Ω cm for the highest dose of 1.5 × 1020 n cm-2. In this high dose region the temperature dependence of the resistivity at low temperatures is given by exp [b/T 1/4] and it is suggested that in this highly disordered state conduction occurs by tunnel-assisted hopping between defect levels in the band gap. The presence of such levels is indicated by the strong optical absorption tail which is produced from 0.1 eV to the crystalline edge at 1.5 eV. Although at the highest doses the samples contain a high degree of disorder, X-ray diffraction shows that they are basically crystalline. Lattice parameter determinations show that it increases with dose, linearly at first, then tending ...
84 citations
TL;DR: In this article, the ordered phases of V3S4 and V5S8 were refined with single crystal data, and short metal-metal bonds were found between the layers as well as within them.
84 citations
TL;DR: In this paper, a cubic perovskite cell for the ideal composition of SrFeO2.75 was found in the powder x-ray diffraction photographs, and a plausible model for the structure is presented which is related to that of the structure of the ideal phase.
79 citations
TL;DR: In this article, the magnetic susceptibility of the β-phase CoGa has been correlated with the defect structure of this phase, and the effective local magnetic moment per TAS -atom was found to be (5.02±0.06)μ B.
75 citations
TL;DR: The high temperature form of silver tungstate, Ag8W4O16, contains tetratungstate ions in which the tungsten atoms are coplanar and each is octahedrally coordinated to oxygen atoms as mentioned in this paper.
73 citations
TL;DR: The effect of high pressure on the crystal structures of LnAl 3 (Ln = Lanthanide) compounds has been determined by exposing the compounds to high pressure and high temperature conditions in a tetrahedral-anvil apparatus.
Abstract: The effect of high pressure on the crystal structures of LnAl 3 (Ln = Lanthanide) compounds has been determined by exposing LnAl 3 compounds or stoichiometric mixtures of the elements, to high-pressure and high-temperature conditions in a tetrahedral-anvil apparatus. In accordance with considerations of relative compressibilities, the application of high pressure tends to make the lower-atomic-weight lanthanides behave more like those of higher atomic weight. Thus, high-pressure-induced polymorphic changes were in the direction of structures with increased cubic character. Polymorphs or compounds first reported in this paper are BaPb 3 -type GdAl 3 , HoAl 3 -type TbAl 3 and Cu 3 Au-type LuAl 3 . The first two are hexagonal with lattice parameters α = 6.231, c = 21.173 A , and α = 6.095, c = 35.96 A , respectively. The third compound is cubic, with lattice parameter α = 4.186 A .
TL;DR: In this paper, the ratio of the two lattice parameters without the need for a precise knowledge of the X-ray wavelength was given by using pseudo non-dispersive MIMO diffractometry with Mo Ka 1 radiation.
Abstract: The d spacing of the 355 reflexion in silicon has been compared with the d spacing of the 800 reflexion in germanium using pseudo non-dispersive multiple-beam X-ray diffractometry with Mo Ka1 radiation. This technique gives the ratio of the two lattice parameters without the need for a precise knowledge of the X-ray wavelength. Symmetric transmission geometry was used to eliminate the refractive index correction. The results were: {{d(800 Ge)}\over{d(355 Si)}} = 1.0002348 (± 0.0000006) at 22.5 °C and {{d(800 Ge)}\over{d(355 Si}} = 1.0002458 ( ± 0-0000016) at 25 °C. By using the known lattice parameter of silicon obtained by X-ray and optical interferometry it was found that the lattice parameter of germanium at 25 °C is 5.6579060 ± 0.0000092 A.
TL;DR: In this paper, the superconducting properties of bulk films (0.02-0.06 mm thick) of Nb 3 Ge deposited on Cu substrates by chemical vapor deposition have been studied along with physical parameters characterizing these deposits.
Abstract: The superconducting properties of bulk films(0.02- 0.06 mm thick) of Nb 3 Ge deposited on Cu substrates by chemical vapor deposition have been studied along with physical parameters characterizing these deposits. Results of susceptibility measurements showing superconducting onsets greater than 21 K and resistivity measurements showing onset greater than 22 K are presented along with heat capacity measurements. Data are also presented defining a relationship between superconducting transition temperature and lattice spacing throughout the range of 4 - 21 K. In addition, the effects of substrate temperature and substrate material, as well as mechanical properties such as substrate adherence are described.
TL;DR: In this paper, the crystal structure of the 1,3-propylenediammonium chloride (POMC) and manganese chloride (MCL) is reported.
TL;DR: In this article, it was shown that a linear combination of at most 8 lattice sums is sufficient to give the Madelung constant of all such lattices, in many cases this reduces to just 3 sums.
Abstract: A method is given of evaluating Madelung constants for invariant cubic lattice complexes. It is shown that a linear combination of at most 8 lattice sums is sufficient to give the Madelung constant of all such lattices. In many cases this reduces to just 3 sums. The 8 sums suffice also to determine the Madelung constant for tetragonal lattices with axial ratio square root 2 or 2 and for orthorhombic lattices with lattice parameters in the ratio 1: square root 2:2. The method developed here is also applied to the evaluation of lattice sums arising from particles interacting with a general r-s potential.
TL;DR: The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 plus or minus 5 C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera.
Abstract: The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 plus or minus 5 C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change in the expansion coefficients for all axes above 400 C. The relative changes in the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl-type structure is observed at 651 plus or minus 5 C. The lattice parameter of the cubic form of GeSe is a 0 ? 5.730 plus or minus 0.003 A at 656 C. The GeSe lattice remains cubic up to the melting point.
TL;DR: In this article, the results of lattice parameter measurements and the linear thermal expansion coefficient of niobium were reported from liquid helium temperature to room temperature, using a commercially available cryostat.
Abstract: The results of lattice parameter measurements and the linear thermal expansion coefficient of niobium are reported from liquid helium temperature to room temperature, using a commercially available cryostat. 2 references.
TL;DR: Mordenite is a zeolite whose approximate composition is (Na2, K2,Ca)4[Al8Si40O96] 28 H2O as mentioned in this paper.
Abstract: Mordenite is a zeolite whose approximate composition is (Na2, K2,Ca)4[Al8Si40O96] 28 H2O. Unit cell dimensions, determined by X-ray powder diffractometry for 35 natural samples, fell within the following ranges: a=18.052–18.168, b=20.404–20.527, c=7.501–7.537 A. The indexed powder pattern of a typical sample is reported. Complete wet chemical analyses of 12 samples, partial analyses of three others, and 6 analyses from the literature reveal that mordenites vary only slightly in chemical composition. Si occupies 80 to 85% of the tetrahedra, and the exchangeable cations are mainly Na and Ca, with minor K. The lattice constant b is negatively correlated to the ratio Si/(Si+Al+Fe‴).
TL;DR: By cooling slowly a homogeneous solution of La, B and Al from about 1200°C, single crystals of lanthanum hexaboride (LaB6) were precipitated, and their lattice constant, purity and growh-orientations were investigated as discussed by the authors.
Abstract: By cooling slowly a homogeneous solution of La, B and Al from about 1200°C, single crystals of lanthanum hexaboride (LaB6) were precipitated, and their lattice constant, purity and growh-orientations were investigated. The products are needle-like crystals with a rectangular cross section, thin plate-like crystals and cubical crystals. The LaB6 crystal has the lattice constant 4.1564A and contains impurities of less than 0.01 wt%. More needle-like crystals with [110] growth direction tend to be formed than any crystals with other shapes. For the typical needle-like crystals, the crystal thickness depends on the cooling rate. The average size is 0.1 to 0.5 mm square in cross section and about 5 mm in length.
TL;DR: In this paper, the use of paramagnetic resonance of dilute Gd impurities as a probe of exchange and crystal-field effects in the singlet ground-state systems was studied.
Abstract: We have studied the use of paramagnetic resonance of dilute Gd impurities as a probe of exchange and crystal-field effects in the singlet-ground-state systems $\mathrm{Tm}X$ and $\mathrm{Pr}X$ (where $X$ is one of the group-$\mathrm{V}A$ elements, P, As, Sb, Bi), i.e., the thulium and praseodymium monopnictides of NaCl structure. Analysis of the temperature-dependent resonance $g$-value behavior yields values for the Gd-Tm and Gd-Pr exchange interactions. The Gd-Tm exchange changes sign with increasing lattice parameter (on going from the phosphide and arsenide to the antimonide and bismuthide); while the Gd-Pr exchange becomes increasingly negative with increasing lattice parameter. Analysis of the temperature dependence of the linewidth yields values for the crystal-field splitting of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ in agreement with those from neutron scattering. We briefly mention recent experiments using EPR of Gd in TbP to probe the behavior of the staggered susceptibility in the critical region.
TL;DR: The magnetic properties of MgCo2, MgNi2 and Mg2Ni were investigated in the range 4-400 K as mentioned in this paper, and the lattice constants were determined.
TL;DR: In this article, the cation distribution and the oxygen parameter for the system Mg1+y Fe2(1−y) Ti 2 y O4 have been determined using the intensities of X-ray reflections.
Abstract: The cation distribution and the oxygen parameter for the system Mg1+y
Fe2(1−y) Ti
y
O4 have been determined using the intensities of X-ray reflections. Results are given for slowly cooled and quanched samples. An explanation is proposed to account for the behaviour of the lattice parameter and the oxygen parameter.
TL;DR: In this article, the influence of the deviation from stoichiometry on the magnetic properties has been investigated on the compositions given by the formula (NiO) α (ZnO) 1-α (Fe 2 O 3 ) x where α = 0.30 ; 0.36 and 0.9 s, T c ), the influence is much lower but unambiguous.
Abstract: The influence of the deviation from stoichiometry on the magnetic properties has been investigated on the compositions given by the formula (NiO) α (ZnO) 1-α (Fe 2 O 3 ) x where α = 0.30 ; 0.36 and 0.9 s , T c ), the influence of the deviation is much lower but unambiguous. It is the variation of the Curie temperature with x which is responsible for the large susceptibility variations (previously mentionned by other authors at room temperature). The variation of T c could be related to the variation of the lattice constant with x.
TL;DR: In this paper, the Nd(IO3)3⋅H2O was shown to have a pyroelectric coefficient at room temperature is about 2.2×10−5 cm−2/°K.
Abstract: Neodymium iodate monohydrate, Nd(IO3)3⋅H2O, crystallizes in the monoclinic system with space group P21 and two formulas in the unit cell. The pyroelectric coefficient at room temperature is about 2.2×10−5 cm−2/°K. The lattice constants at 298°K are a = 10.2012±0.0013, b = 6.70530±0.00004, c = 7.3538±0.0009 A, and β = 113.11±0.02° (λ CuKα1 = 1.540562 A). A total of 8060 reflections were measured within a reciprocal hemisphere having (sin ϑ)/λ ? 1.02 A−1, using PEXRAD. The crystal structure was solved by the interpretation of Patterson and Fourier series and refined by the method of least squares using 2603 independent Fmeas, with final agreement factor R = 0.058. The three independent IO3− ions share oxygen atoms to form a three−dimensional framework of corner−sharing polyhedra. Two iodine atoms are coordinated by seven and the third by six oxygen atoms. All iodine polyhedra have three short I−O distances averaging about 1.81 A, and longer I−O distances ranging to 3.3 A. The water molecule links all three ...
TL;DR: In this paper, a single crystal structure investigation revealed relationships with Ca 2 Nb 2 O 7, Sr 2 NB 2 NB O 7 and La 2 Ti O 7 using X-ray diffraction.
TL;DR: In this article, the Czochralski technique was used to grow single crystals with coupled substitution of calcium and zirconium for gadolinium and gallium at dodecahedral and octahedral sites, respectively.
TL;DR: In this paper, the electrical and optical absorption properties of yttrium iron garnet (YIG) were investigated by means of lattice constant measurements and the defect mechanism was discussed, and a model for the band structure of YIG was proposed and discussed.
TL;DR: In this article, a curve of applied pressure P versus lattice constant a is calculated for single crystal aluminum, based on Fermi surface analysis, which is used to verify that the face-centered cubic structure remains the preferred crystalline phase up to the highest pressures considered.
Abstract: A curve of applied pressure P versus lattice constant a is calculated for single crystal aluminum. It results from an application of the method of structural expansions for deriving the energies of simple metals, a method known to give reasonable results for the elastic constants even at second order in the effective electron-ion interaction. The method is taken from Fermi surface analysis . This essentially experimental information is used to verify that the extant face-centered cubic structure remains the preferred crystalline phase up to the highest pressures considered. Arguments are given to suggest that the P versus a curve should have reasonable a priori accuracy, which may be improved if experimental data in the intermediate pressure region can be provided to refine the energy dependent pseudo-potential. At 3 megabars the lattice constant is reduced by only 22%; the ion cores at this pressure are still very well separated.
TL;DR: In this paper, the lattice parameter during decomposition of a supersaturated solid solution can be used to distinguish pre-precipitation from precipitation in appropriate circumstances, where the solute atoms still diffract with the solvent atoms and the fundamental X-ray diffraction peaks are identical to those of the random supersaturated liquid solution regardless of the manner in which the solutes are distributed among the atomic sites.
Abstract: Measurement of the lattice parameter during decomposition of a supersaturated solid solution can provide a method for distinguishing pre-precipitation from precipitation in appropriate circumstances. During pre-precipitation the solute atoms still diffract with the solvent atoms and the fundamental X-ray diffraction peaks are identical to those of the random supersaturated solid solution regardless of the manner in which the solute is distributed among the atomic sites. Thus, a difference exists between heterogeneities produced by pre-precipitation (zones) and those produced by precipitation of a second phase (precipitates). This principle is illustrated for a wide range of alloy systems and its applicability is discussed.
TL;DR: A-type superconducting compound Nb 3 Si was synthesized by chemical vapour deposition as mentioned in this paper, and the A-15 single phase was obtained in the reaction temperature range between 800° to 900° C.