Showing papers on "Lattice constant published in 1971"
TL;DR: In this article, the atomic positions of Ferroelectric BiFeO 3 were determined using both X-ray single crystal and neutron powder diffraction using the multiple film technique using a Weissenberg camera.
450 citations
TL;DR: In this article, the x-ray scattering by two different rutile crystals, within a hemisphere of reciprocal space having radius (sin θ) /λ=1.02 A−1, was measured at 298°K with PEXRAD.
Abstract: The x‐ray scattering by two different rutile crystals, within a hemisphere of reciprocal space having radius (sin θ) /λ=1.02 A−1, was measured at 298°K with PEXRAD. The integrated intensities of 780 reflections from each crystal were determined, resulting in 136 symmetry independent Fmeas from Crystal 1 and 122 Fmeas from Crystal 2. The crystal structure was refined by the method of least squares: The agreement factor R for all Fmeas is 0.0286, and the single position parameter x(0)=0.30479±0.00010. Normal probability plot analysis shows the least squares derived standard deviations are underestimated by 33%, and the two sets of Fmeas contain an appreciable parallel bias. The lattice constants, measured at or corrected to 298°K on two different crystals, are a=4.593659±0.000019 and c=2.958682±0.000008 A. The Ti–O distances are 1.9800±0.0009 and 1.9485±0.0005 A. Pairs of shorter bonds define O–Ti–O angles of 81.21° and 98.79°, forming a plane normal to the two longer bonds. The resulting octahedral Ti–O bo...
277 citations
TL;DR: Ferroelectric K(6−x−y)Li(4+x)Nb(10+y)O30, with x ≥ 0.07, y ≤ 0.23, and a Curie temperature of 613°K, crystallizes with a tungsten bronze-type structure in the tetragonal system as mentioned in this paper.
Abstract: Ferroelectric K(6−x−y)Li(4+x)Nb(10+y)O30, with x ≃ 0.07, y ≃ 0.23, and a Curie temperature of 613°K, crystallizes with a tungsten bronze‐type structure in the tetragonal system. The lattice constants are a = 12.5764 ± 0.0002 and c = 4.0149 ± 0.0001 A at 298°K. The space group is P4bm. There is one formula per unit cell. The integrated intensities of 6578 structure factors, inside a reciprocal hemisphere of radius (sinθ) / λ = 1.02 A−1, were measured with PEXRAD. There are 998 symmetry‐independent Fmeas significantly above background. Isomorphism with BaxSr(5−x)Nb10O30 allowed the metal atom positions to be deduced. Oxygen atom positions were obtained by Fourier series methods. Refinement of structural parameters by the method of least squares resulted in a final agreement factor R = 0.0401. The structure is generally like that of other tungsten bronzes of formula (A1)2(A2)4C4(B1)2(B2)8O30, with the A1 site occupied by 87% K and 13% Li, the A2 site by 99% K and 1% Li, and the C site by 94% Li and 6% Nb. Th...
172 citations
TL;DR: In this paper, the LEED structures resulting from hydrogen adsorption on (100)W are studied as functions of hydrogen coverage and surface temperature for temperatures above 78 °K, and it is suggested that this structure on the clean surface may be due to structural rearrangement of tungsten or an adsorbed state of hydrogen which goes into solution upon heating.
143 citations
TL;DR: In this paper, the authors consider the effect of pair interaction of solute atoms and electronic constitution on the lattice spacing of Pd or Fe at constant pressure, i.e., constant volume rather than constant pressure.
126 citations
TL;DR: In this paper, a superimposed rf current, whose frequency is a harmonic or subharmonic of the ratio of the vortex velocity and the lattice parameter, is reported.
Abstract: An experimental study is reported of steps induced in the flux-flow $I\ensuremath{-}V$ characteristics of superconducting aluminum films by a superimposed rf current, whose frequency is a harmonic or subharmonic of the ratio of the vortex velocity and the lattice parameter.
123 citations
TL;DR: In this paper, the Patterson and Fourier series was used to solve β-Gadolinium molybdate (Gd2(MoO4)3) and the final agreement factor R is 0.089 based on isotropic thermal vibrations.
Abstract: Beta‐gadolinium molybdate, β‐Gd2(MoO4)3, is ferroelectric and ferroelastic with a Curie temperature of about 160°C and is paramagnetic with a moment of 7.98 μB. β‐Gd2(MoO4)3 crystallizes in the orthorhombic system with space group Pba2 and four formulas in the unit cell. The lattice constants at 298°K are a = 10.38582 ± 0.00014, b = 10.41861 ± 0.00010, and c = 10.70039 ± 0.00004 A. The integrated intensities of 14 490 reflections were measured with PEXRAD, within a hemisphere of reciprocal space of radius (sinθ) / λ = 1.02 A−1. The crystal structure was solved by interpretation of Patterson and Fourier series and refined by the method of least squares, using a total of 2545 symmetry independent Fmeas. The final agreement factor R is 0.089, based on isotropic thermal vibrations for all atoms. X‐radiation exposure introduces appreciable nonrandom error in the Fmeas. The structure consists of three crystallographically independent discrete sets of (MoO4)2− tetrahedra; one set is oriented with apex oxygen ato...
109 citations
TL;DR: CdSiP2 as discussed by the authors is a typical member of the AIIBIVC2V family with chalcopyrite structure and the lattice constants of this tetragonal crystal are a
Abstract: CdSiP2 is a typical member of the AIIBIVC2V family with chalcopyrite structure. The x‐ray scattering for luminescent and nonluminescent material is essentially identical: The atomic order at the Cd and Si sites is at least 99.8% complete. The lattice constants of this tetragonal crystal are a = 5.680 ± 0.001 and c = 10.431 ± 0.003 A at 298°K. The space group is I42d, and there are four formulas per unit cell. A total of 2370 reflections from a nonluminescent crystal, and 2156 from a luminescent CdSiP2 crystal, were measured with PEXRAD. Least squares refinement, based on 320 symmetry‐independent reflections from both crystals, led to a final agreement factor of 0.047. Normal probability plot analysis shows the least squares derived standard deviations to be underestimated by a factor of 3.0, and the two sets of measured structure factors to possess a small parallel bias. The bond angles about the Si atom do not differ significantly from the regular tetrahedral angle of 109.47°. Regular tetrahedral bond a...
94 citations
TL;DR: In this article, superconducting transition temperature data are presented as a function of the β-W lattice constant in NbGa alloys, and the stoichiometric material is obtained by quenching from above a solidus followed by a low temperature anneal.
89 citations
TL;DR: In this article, a tentative phase diagram has been constructed for the Sm-Fe system and three compounds have been observed: SmFe 2 (MgCu 2 -type), SmFe 3 (PuNi 3 -type) and Sm 2 Fe 17 (Th 2 Zn 17 -type).
Abstract: The Sm-Fe system has been investigated by X-ray diffraction, thermoanalysis and metallography. Three compounds have been observed: SmFe 2 (MgCu 2 -type), SmFe 3 (PuNi 3 -type) and Sm 2 Fe 17 (Th 2 Zn 17 -type). Their lattice constants and Curie temperature have been determined. A tentative phase diagram has been constructed.
87 citations
01 Feb 1971
TL;DR: In this article, it was shown that Schenck and Stein this article showed that the shape of the diffusion table can be approximated by roughly joining the points in the pe r iodic table.
Abstract: whe re M i s the m o l e c u l a r weight . T h e s e c~ )va lues a r e given in Tab le I. F i g s . 1 and 2 and Tab le I w e r e p r e pared in this way, because this p r o c e d u r e was m o s t convenient fo r use in the diffusion r e s e a r c h , to be r e por ted l a t e r . The e l e m e n t s T i , Rh, Pd, and Ge w e r e not involved d i r ec t l y in the diffusion s tudy, thus do not appea r in F ig s . 1 and 2, however , they w e r e l a t e r added to Tab le I by ca lcu la t ion f r o m rev i ew pape r r e f e r e n c e s . 2 It is to be noted that the t e r m (MFe -,~//x)//MFe of Eq. [1] has not been applied by ce r t a in au tho r s , in ca l cu la t ing e~); this m a k e s a v e r y impor t an t d i f f e rence fo r many e l e m e n t s and indeed may account fo r c e r t a i n r e la t ions not being r e p o r t e d be fo re . F ig . 3 shows the r e s u l t obtained by plot t ing ~ ) v s a tomic no. of e l emen t x, and with r e s p e c t to th ree pe r iods in the pe r iod ic table . The shape of the f i gu re , made by roughly joining the points , r e p e a t s i t se l f gene r a l l y in the pe r iods and m o v e s upwards in pass ing f r o m the f i r s t long per iod to the th i rd long per iod . The c o r r e l a t i o n is admi t ted ly ske tchy, pa r t ly because only fou r t een e l e m e n t s a re involved, but t he re a re enough data to see it taking shape. Although m o r e and s o m e t i m e s be t t e r data a r e needed to ref ine this r e l a t ionsh ip , it does appea r that it may be used with a somewha t g r e a t e r deg ree of conf idence than Schenck and Ste inm e t z ' s l i n e a r one fo r p red ic t ing i n t e r a c t i o n coe f f i c i en t s
TL;DR: In this article, the structure of NdVO 4 was refined from single-crystal X-ray diffraction data and the positional parameters for a series of vanadates were calculated by minimizing the lattice energy with respect to u and v, assuming the experimental space group and lattice parameters.
TL;DR: In this paper, the existence of a 3D defect array in high purity molybdenum, and in T.Z.M., irradiated at high temperatures with 2 MeV nitrogen ions to doses of approximately 1018 ions/cm2.
Abstract: Electron microscope observations are presented to demonstrate the existence of a three-dimensional defect array in high purity molybdenum, and in T.Z.M., irradiated at high temperatures with 2 MeV nitrogen ions to doses of approximately 1018 ions/cm2. It is shown that the defect array has a body centred cubic structure with a ‘lattice parameter’ of 220 A and with crystallographic axes coincident with those of the molybdenum matrix. The identification of the defects as voids is discussed together with possible mechanisms for the array formation.
TL;DR: In this article, the effect of lattice parameter mismatch on the spacing and configuration of dislocations at the interface between phases was studied in directionally solidified eutectics.
TL;DR: In this article, the lattice parameters of Gd, Tb, Dy, Ho, Er, Tm, Lu, Y and Sc were determined on well-characterized samples.
Abstract: The common methods presently used to prepare samples of the heavy rare-earth metals for lattice parameter determinations were shown to give high results due to contamination by interstitial impurities, especially hydrogen. Two methods to produce fine-grained homogeneous samples in the form of wires were established. Both methods have the advantage of not requiring further heat treatment after preparation of the surface to be X-rayed. The lattice parameters of Gd, Tb, Dy, Ho, Er, Tm, Lu, Y and Sc were determined on well-characterized samples. The density, mole atomic volume, atomic radius for CN12, and c a ratios were calculated based on the lattice parameters determined. The effect of hydrogen on the lattice parameters of these metals was determined.
TL;DR: In this article, three titanomagnetite samples, of composition x=0.7, 0.9, and 1.0, were oxidized according to the method of Sakamoto et al., namely, wet grinding followed by heating to 200-300°C.
Abstract: Three titanomagnetite samples, of composition x=0.7, 0.9, and 1.0 (where x is the ulvospinel molecular fraction), were oxidized according to the method of Sakamoto et al., namely, wetgrinding followed by heating to 200–300°C. Like the samples of Sakamoto et al., our samples showed reversal of saturation magnetization during alteration of titanomagnetite to titanomaghemite. Our experimental results seem to be compatible neither with the ionic model of Verhoogen nor with the model of O'Reilly and Banerjee. The Curie point gradually increased and the lattice parameter decreased during low-temperature oxidation (titanomaghemitization). On heating above 300°C, the γ-titanomaghemites underwent high-temperature oxidation (unmixing into magnetite, pseudobrookite, which is formed only during heating to 600°C, and rutile phases). The unmixing results in a sudden increase in Curie point and decrease in lattice parameter and saturation magnetization. On further heating, the saturation magnetization reverses for a second time. Therefore, double self-reversal of remanent magnetization in naturally oxidized rocks is considered a real possibility.
01 Mar 1971
TL;DR: In this paper, the effect of aluminum and iron on the formation of transitional phases has been examined for alloys of the Ni-Nb system, and it has been established that metastable phases of approximate composition Ni3Nb will not form in binary NiNb alloys under normal conditions of quenching and aging, but that iron or iron and aluminum additions promote their formation when certain size and electronic factors are satisfied.
Abstract: The effect of additions of aluminum and iron on the formation of transitional phases has been examined for alloys of the Ni-Nb system. It has been established that metastable phases of approximate composition Ni3Nb will not form in binary Ni-Nb alloys under normal conditions of quenching and aging, but that iron or iron and aluminum additions promote their formation when certain size and electronic factors are satisfied. In Ni-Nb-Fe alloys containing more than ≈ 12 at. pct Nb, iron promotes the formation of a bct (DO22) Ni3Nb precipitate. Aluminum additions to these Ni-Nb-Fe alloys promote the precipitation of fcc (L12) Ni3Nb γ’, initially together with the bct phase, but at higher aluminum concentrations the tetragonal phase disappears. The appearance of both precipitates followed the Hagel-Beattie requirement for interfacial mismatch of < or ∼ 1 pct between the matrix and the precipitate. The presence of both precipitating phases can be predicted on the basis of the Engel-Brewer correlations. The preferrede/a ratio for the stability of the bct (DO22) phase is 2.50 to 2.62. In the present investigation this phase precipitates only in the presence of iron (bcce/a ratio = 1.5), and only when the lattice constant of the matrix is greater than 3.600A. The preferrede/a ratio for the stability of the γ’ having a fcc L12 structure is between ∼2.75 and 3.0. Precipitation of this phase occurred only when aluminum(e/a) ratio = 3.0) was present, and when the matrix lattice constant was greater than 3.589A.
TL;DR: The results of a study of the magnetic properties of the hexaborides of cerium, praseodymium, europium, and gadolinium at temperatures from 7 to 300 °K are reported in this article.
Abstract: The results of a study of the magnetic properties of the hexaborides of cerium, praseodymium, europium, and gadolinium at temperatures from 7 to 300 °K are reported. The susceptibility of CeB6 obeys a Curie-Weiss law, χ = C/(T – θ), above 200 °K with a moment of 2.51 μβ and θ = −82 °K. PrB6 obeys a Curie-Weiss law above 100 °K with a moment of 3.64 μβ and θ = −41 °K. The reciprocal susceptibility of PrB6 shows a minimum at 8.3 °K associated with an antiferromagnetic transition. Europium hexaboride is ferromagnetic at low temperatures with a Curie point of 8.8 °K. The initial reciprocal susceptibility in the range from 9 to 14 °K varies at (T – TC)1,20. Above 30 °K the susceptibility of EuB6 accurately obeys a Curie-Weiss law with θ = −0.5 °K and μeff = 7.90 μβ. Magnetization curves and isotherms of σ2 vs. H/σ are given for EuB6 for temperatures just above the Curie point. The susceptibility of GdB6 obeys a Curie-Weiss law above 70 °K with θ = −66.5 °K and μeff = 7.98 μβ. Further, an antiferromagnetic transition exists at (16.4 ± 0.2) °K. Finally, X-ray diffraction data were obtained for the four compounds yielding lattice constants of 4.140 A, 4.131 A, 4.175 A, and 4.109 A for CeB6, PrB6, EuB6, and GdB6 respectively.
Es wird uber die Ergebnisse einer Untersuchung der magnetischen Eigenschaften der Hexaboride des Zer, Praseodym, Europium und Gadolinium bei Temperaturen von 7 bis 300 °K berichtet. Die Suszeptibilitat des CeB6 folgt oberhalb 200 °K dem Curie-Weiss'schen Gesetz χ = C/(T – θ) mit einem Moment von 2,51 μβ und θ = −82 °K. PrB6 folgt oberhalb von 100 °K einem Curie-Weiss-Gesetz mit einem Moment von 3,64 μβ und θ = −41 °K. Die reziproke Suszeptibilitat von PrB6 zeigt bei 8,3 °K ein Minimum, das mit einem antiferromagnetischen Ubergang verbunden ist. Europiumhexaborid ist bei tiefen Temperaturen ferromagnetisch mit einer Curie-Temperatur von 8,8 °K. Die reziproke Anfangssuszeptibilitat variiert im Bereich von 9 bis 14 °K wie (T – TC)1,20. Oberhalb von 30 °K befolgt die Suszeptibilitat von EuB6 exakt ein Curie-Weiss-Gesetz mit θ = −0,5 °K und μeff = 7,90 μβ. Magnetisierungskurven und Isothermen von σ2 als Funktion von H/σ werden fur EuB6 fur Temperaturen wenig oberhalb der Curie-Temperatur mitgeteilt. Die Suszeptibilitat von GdB6 folgt einem Curie-Weiss-Gesetz oberhalb 70 °K mit θ = −66,5 °K und μeff = 7,98 μβ. Ferner existiert ein antiferromagnetischer Ubergang bei (16,4 ± 0,2) °K. Rontgenbeugungsuntersuchungen der vier Verbindungen ergaben Gitterkonstanten von 4,140 A, 4,131 A, 4,175 A bzw. 4,109 A fur CeB6, PrB6, EuB6 bzw. GdB6.
TL;DR: In this paper, a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice is presented, and the results predict that a void lattice should occur in molybdenum and compare a number of models for the void.
Abstract: Defects in crystals may form a regular array, rather than a random distribution. The lattice of voids produced in irradiated molybdenum is a remarkable example of this. We give a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice. The existence of the void lattice depends on the elastic interaction between voids. The present approach can treat both arbitrarily anisotropic elastic continua and discrete lattices, and is readily extended to discuss the stability of the defect lattice. The results predict that a void lattice should occur in molybdenum, and compare a number of models for the void. Stability against shear of the void lattice is not discussed in the present paper. The ratio of the void lattice spacing to void radius predicted is 2.2 to 4.5 and is smaller than the value of about 10 observed. The results are in general agreement with the more approximate Malen-Bullough treatment.
TL;DR: In this paper, the authors reported that the ratio of the number of holes per tin-vacancy acceptor to the 77 K Hall factor is independent of the apparent hole concentration.
01 Dec 1971
TL;DR: In this article, a new model is presented which makes it possible to predict the lattice parameters of metallic solid solutions as a function of composition, based on the hypothesis that the measured lattice parameter of a solid solution alloy is the average of all the interatomic spacings within a selected region of a lattice.
Abstract: A new model is presented which makes it possible to predict the lattice parameters of metallic solid solutions as a function of composition. This method is based on the hypothesis that the measured lattice parameter of a solid solution alloy is the average of all the interatomic spacings within a selected region of the lattice.
TL;DR: The effects of self-irradiation damage induced in 244CmO2 have been studied by following the evolution of the lattice parameter of this compound as a function of time.
TL;DR: In this paper, the defect structure of β NiAl is investigated, with copper substituted for nickel in fixed concentration ratios x Ni Cu and in Ni 1−yCuyAl. The number of nickel vacancies is increased due to the addition of copper to the alloy, as is shown by lattice spacing and density measurements.
TL;DR: In this paper, X-ray crystallographic, magnetic, and neutron diffraction and transport properties have been made of the system Cr 1- x Mn x As (0≤ x ≤ 0.9).
Abstract: Studies on X-ray crystallographic, magnetic, neutron diffraction and transport properties have been made of the system Cr 1- x Mn x As (0≤ x ≤0.9). All the members of the system undergo a transition from MnP structure to NiAs structure. Magnetic measurements have revealed the existence of three distinct magnetic regions and the magnetic structures of these regions have been found from neutron diffraction measurements. On the basis of these experimental data, magnetic and crystallographic phase diagrams have been constructed. In particular, CrAs exhibits a discontinuous change in the lattice constants at the Neel temperature which was obtained to be 265°K. The electrical resistivity and thermoelectric power show a strong anomaly at the temperature where the magnetic order disappears. The observed helical spin arrangement may be stabilized by the distorion of the Fermi surface which is caused by the formation of a new zone boundary.
TL;DR: In this article, the resistivity ratios of IrO2 and RuO2 were determined at room temperature and the morphology of the crystals was generally rod-like; extensive twinning was often observed.
TL;DR: In this paper, a method was described whereby intermetallic phases which are not stable at high temperatures may be formed using controlled vacuum evaporation of the elements, and V 3 Al with the A15 structure was formed on substrates held at temperatures in the range 350-450°C.
TL;DR: Some properties dependent on deviations from ideal stoichiometry in Ca 10 (PO 4 ) 6 Cl 2 have been studied in this paper, showing that up to 23% of the CaCl 2 content can be lost without the appearance of a second phase.
TL;DR: Ammonium iodate, NH4IO3, is pyroelectric at room temperature and crystallizes in the orthorhombic system with space group Pc21n and four formulas in the unit cell as mentioned in this paper.
Abstract: Ammonium iodate, NH4IO3, is pyroelectric at room temperature and crystallizes in the orthorhombic system with space group Pc21n and four formulas in the unit cell. The lattice constants at 297°K are a = 6.4115 ± 0.0005, b = 9.1706 ± 0.0005, and c = 6.3740 ± 0.0005 A. The integrated intensities of 4591 reflections within a hemisphere of reciprocal space of radius (sinθ) / λ = 1.02 A−1 were measured using PEXRAD. The crystal structure was solved by Patterson and Fourier series and refined by the method of least‐squares using 1458 symmetry independent Fmeas. The final agreement factor R is 0.054, based on a model with anisotropic iodine and oxygen and isotropic nitrogen thermal vibrations, and with a spherical distribution of hydrogen around the nitrogen atom. The structure consists of discrete IO3− pyramidal ions arranged to give a highly distorted octahedral environment about the iodine. The IO3− ions and NH4− ions form chains parallel to the polar axis. Three I–O distances are in the range 1.765–1.836 A a...
TL;DR: An automatic method of precision lattice parameter measurement, capable of repeated measurement at intervals across single crystals with an accuracy of better than one part in 106, has been applied to gallium arsenide.
Abstract: An automatic method of precision lattice parameter measurement, capable of repeated measurement at intervals across single crystals with an accuracy of better than one part in 106, has been applied to gallium arsenide. The technique has been used to compare homogeneity of material grown from the melt with that prepared by vapour and liquid epitaxy, to study material grown from the melt under various pressures of arsenic, and to investigate the effect of heavy doping on the lattice parameter. The technique is shown to provide new and interesting information on defects in gallium arsenide.
IBM1
TL;DR: In this article, the properties of films grown by liquid phase epitaxy on Czochralski Gd-Ga garnet (111) substrates are discussed, which can be interpreted as being the result of a lattice mismatch stress mechanism.