Showing papers on "Orthorhombic crystal system published in 1970"
TL;DR: In this article, the martensitic transformations involved were studied by X-ray diffraction and the composition dependence of the Martensitic-transformation characteristics, such as Ms, Mf, As and Af-temperatures, were determined.
Abstract: Alloys of compositions near AuTi, PdTi, and PtTi are B19-type orthorhombic at room temperature and, at higher temperatures, have an ordered CsCl-type structure (B2-type). The martensitic transformations involved were studied by X-ray diffraction. The composition dependence of the martensitic-transformation characteristics, such as Ms, Mf, As and Af-temperatures, were determined. Lattice constants of the high-temperature phases are given.
262 citations
TL;DR: In this paper, the crystal structure of poly-e-caprolactone was determined by interpretation of X-ray diffraction patterns, showing that the CH2 sequences are planar but the plane of atoms of the ester group tilts slightly to the fiber axis.
Abstract: In the course of structural studies of aliphatic polyesters, the crystal structure of poly-e-caprolactone, [–(CH2)5–CO–]n, was determined by interpretation of X-ray diffraction patterns. The crystallographic data are: a=7.47A, b=4.98A, c(fiber axis) =17.05A, the orthorhombic space group P212121-D24, two molecular chains in the unit cell. The chain conformation of poly-e-caprolactone is almost planar zigzag, but evidently deviates from the fully extended form, i.e., the CH2 sequences are planar but the plane of atoms of the ester group tilts slightly to the fiber axis. The molecular chains are arranged side by side in the same way as in polyethylene, but the carbonyl groups of the two chains in the unit cell are separated by an amount of 3/14c along the fiber axis.
254 citations
TL;DR: In this article, the properties of perovskite-type oxide LaMnO 3 were studied experimentally and theoretically using a phenomenological approach or the Spin-Hamiltonian formalism.
Abstract: Magnetic properties of the perovskite-type oxide LaMnO 3 were studied in detail, experimentally and theoretically. The properly stoichiometric LaMnO 3 had a weak ferromagnetic moment in addition to the antiferromagnetic character with a Neel temperature of 141°K. It was found to be a parasitic weak ferromagnet. These results can be successfully explained using a phenomenological approach or the Spin-Hamiltonian formalism. The theoretical results show that the antiferromagnetic spin axis should be along the b -axis of the orthorhombic crystal axes and the ferromagnetic moment along the c -axis. The relation between a layer-type ( A -type) antiferromagnetic superexchange interaction and the Jahn-Teller distortion of Mn 3+ ions is also discussed.
217 citations
TL;DR: In this article, the Verwey transition is removed by measuring untwinned single crystals in a magnetic field, and the single crystal spectrum is then resolved into five individual components corresponding to a tetrahedral Fe +3, two octahedral Fe+3 and two octagonal Fe +2 sites.
145 citations
TL;DR: In this article, it was proposed that the distortion arises from a Jahn Teller splitting of an accidently degenerate pair of low lying Dy3+ doublets, which is correlated with the direction of principal g value and can be influenced by applied magnetic fields.
129 citations
TL;DR: In this paper, X-ray diffraction has been used to determine the crystal structure of poly(vinylidene fluoride) phase II, and three principal chain conformations were considered, which included two 21 helical forms [degenerate (planar) and nondegenerate] and the trans-gauche-trans-gaueche' form.
Abstract: In this study, X-ray diffraction has been used to determine the crystal structure of poly(vinylidene fluoride) phase II. Three principal chain conformations were considered, which included two 21 helical forms [degenerate (planar) and nondegenerate] and the trans-gauche-trans-gauche' form. An X-ray crystal structure determination has shown that the trans-gauche-trans-gauche' (TGTG′) conformation is the correct one for phase II. Experimental X-ray intensity data were taken at both −145° and 20° C in order to study the effect of temperature on the resulting structure. From the comparison between observed and calculated intensities, there are two possible crystal symmetries, P21 and P1, depending upon whether the two chains are taken to be antiparallel or parallel to one another. For both cases, the reliability indices for the chosen structure are almost identical. For either symmetry the unit cell is metrically orthorhombic (all angles equal to 90° within experimental error) with the following latt...
115 citations
TL;DR: In this article, a number of electrical, optical and mechanical measurements on ferroelectric Gd2(MoO4)3, are presented based on which it is concluded that the symmetry in the paraelectric phase above 159°C is tetragonal 42m and the symmetry below the transition is orthorhombic mm2.
Abstract: Results of a number of electrical, optical and mechanical measurements on ferroelectric Gd2(MoO4)3, are presented Based on these results it is concluded that the symmetry in the paraelectric phase above 159°C is tetragonal 42m, and the symmetry below the transition is orthorhombic mm2. Twin walls are shown to be ferroelectric domain walls with the relationship between the polarity of the spontaneous polarization P, and the relative positions of the orthorhombic a and b axes being dictated by the piezoelectric effect in the paraelectric phase. A large mechanical dimension change and large optical effects accompanying ferroelectric switching are discussed and possible applications of these effects are considered briefly.
94 citations
TL;DR: The ternary phase fields of three tetragonal tungsten-bronze type structures have been located as mentioned in this paper, and only one of these structures is a Ternary compound; it is located along the binary join, extending from 20 to 80 m/o, and melts congruently near 50%.
Abstract: Phase equilibria in the binary system and the ‐rich region of the ternary system were investigated by DTA, x‐ray diffraction, strip heater, and Curie temperature measurement techniques. The ternary‐phase fields of three tetragonal‐tungsten‐bronze type structures have been located, Only one of these structures is a ternary compound; it is located along the binary join, extending from 20 to 80 m/o , and melts congruently near 50% . The ternary solubility extends from about 4% excess to about 1% excess . This phase possesses observable orthorhombic distortion in the ‐rich region of the solid solution. The implications of the phase diagram for the crystal growth of these compounds are briefly discussed.
81 citations
TL;DR: In this article, a new high-pressure form of Rh2O3 has been prepared at 65 k bar and 1200°C, and four-probe resistivity measurements made on a single crystal show that it is a semiconductor with a room-temperature resistivity of 130 Ω cm and an activation energy of 0.16 eV.
77 citations
TL;DR: In this article, the Madelung Part of Lattice Energy (MAPLE) is calculated and discussed, and the MADELung-Anteil der Gitterenergie wird berechnet und diskutiert.
Abstract: Nach Einkristalldaten (137 h 01, h 11, h 21; Mo—Kα) kristallisiert Li2CuO2 (weinrote Kristalle) orthorhombisch mit a = 3,663, b = 2,863, c = 9,396 A, Z = 2, D—Immm mit Li in (4j), Cu in (2b), O in (4i) und z = 0,293, z = 0,3565. Der Madelung-Anteil der Gitterenergie (MAPLE) wird berechnet und diskutiert.
According to single crystal data [137 h 01, h 11, h 21; Mo—Kα] Li2CuO2 (ruby) crystallizes orthorhombic with a = 3.663, b = 2.863, c = 9.396 A; Z = 2, D—Immm; Li in (4j), Cu in (2b), O in (4i) and z = 0.293, z = 0.3565. The Madelung Part of Lattice Energy (MAPLE) is calculated and discussed.
71 citations
TL;DR: The crystal structure of triphenylphosphine oxide has been determined from three-dimensional X-ray diffraction data, by the symbolic-addition phase-determination procedure as mentioned in this paper.
Abstract: The crystal structure of triphenylphosphine oxide has been determined from three-dimensional X-ray diffraction data, by the symbolic-addition phase-determination procedure. The compound crystallises in the orthorhombic space group, Pbca, with a= 29·120, b= 9·143, c= 11·252 A, and Z= 8. The structure was refined by the full-matrix least-squares method to R 7·8%. Some bond lengths in the crystal are: P–O 1·46 and P–C (mean) 1·76 A.
TL;DR: The crystal structure of Me3SnNCS has been determined by single crystal X-ray diffraction as mentioned in this paper, and the crystals are orthorhombic, Pbca, a = 13.20(1), b = 10.28 (1), c = 12.01(1) A, Z = 8.
TL;DR: In this article, a distorted square planar coordination for copper in which the CuCl 2 angle is 146.13 ± 0.09° and the four bond lengths are: 2.283±0.003A for CuCl(1), 2.290± 0.004 A for the two equivalent CuO bonds.
TL;DR: In this article, birefringence and refractive indices were measured in the orthorhombic, tetragonal and cubic phases of a perovskite material and the dispersion of the refractive index was discussed in terms of a singleoscillator model.
Abstract: Measurements of birefringence and refractive indices in KNbO3 were performed in the orthorhombic, tetragonal and cubic phases. KNbO3 is phase matchable and collinear phase matching is possible for a Nd-laser. Absorption measurements reveal an exponential law for the absorption coefficient (Urbach tail). The dispersion of the refractive indices is discussed in terms of a single-oscillator model. The parameters obtained are in good agreement with those of other perovskite materials. Relations for the electrooptic effect in an orthorhombic oxygen-octahedron ferroelectric are derived and it is found that this effect can explain the observed temperature dependence of refractive indices. Finally, the coefficients for the linear electrooptic effect are calculated and discussed.
TL;DR: Barium cobalt fluoride, BaCoF4, ferroelectric and paramagnetic at room temperature, crystallizes in the orthorhombic system with lattice constants a = 5.8519
Abstract: Barium cobalt fluoride, BaCoF4, ferroelectric and paramagnetic at room temperature, crystallizes in the orthorhombic system with lattice constants a = 5.8519 ± 0.0003, b = 14.628 ± 0.002, and c = 4.2102 ± 0.0003 A at 298°K and space group A21am. The integrated intensities of 1526 reflections within a hemisphere of reciprocal space of radius (sinθ) / λ = 1.02 A−1 were measured with one crystal, and 2986 reflections with a second crystal of BaCoF4, using PEXRAD. The crystal structure was refined by the method of least squares, using 386 symmetry‐independent Fmeas from the first crystal and 875 from the second. The combined set of 1261 Fmeas, together with anisotropic thermal coefficients for all atoms, resulted in a final agreement factor R = 0.0679. The structure is isomorphous with BaMnF4 and contains CoF6 octahedra sharing corners to form puckered sheets parallel to (010). These sheets are linked by Ba2+ ions only. The octahedra are distorted, with Co–F distances ranging from 1.972 to 2.109 A, with an av...
TL;DR: The orthorhombic compounds BaMF4 (Mn, Fe, Co, or Ni) have recently been found to undergo antiferromagnetic transitions at low temperatures as mentioned in this paper.
Abstract: The orthorhombic compounds BaMF4 (M=Mn, Fe, Co, or Ni) have recently been found to undergo antiferromagnetic transitions at low temperatures. Susceptibility measurements on BaNiF4 reveal that a broad maximum occurs at about 150°K similar to that observed in a number of layer‐type structures. As the temperature is lowered, χ∥ along b decreases rapidly, while χ⊥ goes through a shallow minimum around 50°K. At 77°K, no magnetic order can be detected in powder neutron diffraction patterns of BaNiF4, but at 4.2°K there are magnetic peaks which can be indexed on a unit cell doubled along the b and c directions (A21am orientation). The magnetic structure consists of puckered (010) sheets within which the moments are coupled antiparallel to neighboring moments about 4‐A apart. However, the crystal structure is such that the net interaction between adjacent sheets is zero, and ordering in the b direction depends upon interactions between second nearest sheets 14‐A apart. This is very similar to the situation in K2N...
TL;DR: K2MoO4, K2WO4 and Rb2SO4 are monoclinic and isomorphous with orthorhombic cell consts as discussed by the authors.
Abstract: K2MoO4, K2WO4, Rb2MoO4, and Rb2WO4 are monoclinic and isomorphous: Cs2MoO4 and Cs2WO4 are isomorphous with orthorhombic b-K2SO4. Cell consts. and at. parameters are calcd. from powder data, and the powder patterns are given. [on SciFinder (R)]
TL;DR: In this article, the observed fundamentals of the cubic form of As4O6(arsenolite) are unambiguously assigned from single-crystal measurements. But the cage structure is retained in the gas phase.
Abstract: The observed fundamentals of the cubic form of As4O6(arsenolite) are unambiguously assigned from single-crystal measurements. Data are also reported for the isomorphous senarmonite (Sb4O6) which (in the mineral) contains small quantities of the orthorhombic polymorph valentinite (Sb4O6). The gas-phase Raman spectra of P4O10, P4O6, and As4O6(together with polarization data) suggest that the cage structure is retained in the gas phase.
TL;DR: In this article, it was shown that the compounds ThCu 6 and RCu 6, with R = Pr, Nd, Sm, Gd are isotypic and have the orthorhombic CeCu 6 type of structure.
Abstract: A number of rare-earth-copper alloys and thorium-copper alloys near 86 at.% Cu have been investigated by X-ray diffraction. It is shown that the compounds ThCu 6 and RCu 6 , with R = Pr , Nd, Sm, Gd are isotypic and have the orthorhombic CeCu 6 type of structure. For R = Tb and Dy no stable compound of this structure type exists.
TL;DR: In this article, the antimony trifluoride structure was refined to R 0·072 for 370 reflections, with a distorted octahedral co-ordination around an antimony atom.
Abstract: Crystals of antimony trifluoride are orthorhombic, space group C2cm, a= 4·95, b= 7·46, c= 7·26 A, as previously reported. The structure was refined by three-dimensional least-squares methods, to R 0·072 for 370 reflections. Each antimony atom has three close fluorine neighbours with mean Sb–F distances 1·92 A. These SbF3 units are then linked through three fluorine bridges (Sb⋯F 2·61 A) to form a three-dimensional network, with a much distorted octahedral co-ordination around the antimony atom.
TL;DR: In this article, the Laue symmetries of the low temperature phases are masked by the effects of two types of domains on the observed intensities, and it was necessary to solve all three crystal structures.
Abstract: PrAlO3 undergoes a first-order phase transformation at 205°K, and a second order transformation at 151°K. Single crystal X-ray measurements at 293°K, 172°K, and 135°K display the Laue symmetries \overline 3m, mmm, and 2/m respectively. With a specimen ground to a thin crystal plate, and mounted with minimal mechanical restraints, the 205°K transformation was single crystal to single crystal; the 151°K transformation was single crystal to twinned crystal. Both transformations were completely reversible with no sign of fatigue; the twinned crystal always transformed back to a single crystal. The true space group symmetries of the low temperature phases are masked by the effects of two types of domains on the observed intensities. The most probable space groups, expressed in unconventional orientations to preserve continuity with the ideal perovskite structure, are: at 293°K F\overline 32/c, α = 90°21′, V/8 = 53.56 A3, at 172°K I112/m, γ = 90°, V/4 = 53.22 A3, at 135°K I\overline 1, α = γ = 90°, β = 90°40′, V/4 = 53.02 A3. To unravel the true symmetries it was necessary to solve all three crystal structures. The first order transformation is characterized by a shear of (0k0) planes along the rhombohedral [101] direction to form an orthogonal space lattice. The AlO6 groups are rotated into new orientations and Pr atoms are subjected to displacements which are normal to the shear direction. The Pr displacements lower the symmetry from orthorhombic to monoclinic even though the space lattice is orthogonal. The second order transformation is characterized by a shear of (00l) planes along ±[100] in the orthogonal space lattice to form twinned monoclinic space lattices. The AlO6 groups do not assume new orientations. The Pr displacements are increased, again in directions normal to the shear directions. Because of the Pr displacements the symmetry is triclinic even though the space lattice is monoclinic.
TL;DR: In this paper, the existence of a piezoelectric surface wave in cubic and orthorhombic crystals of 23 and 43m classes and mm2 classes is reported.
Abstract: The existence of a piezoelectric surface wave, which does not arise in nonpiezoelectric materials has been reported in hexagonal crystals by Bleustein and Gulyaev. In this letter, similar waves are reported to exist in cubic crystals of 23 and 43m classes and orthorhombic crystals of mm2 class. Velocity equations for the piezoelectric surface waves in these symmetry classes are presented. It has been demonstrated that the velocities are always smaller than the piezoelectrically stiffened but always larger than the unstiffened bulk shear waves in the corresponding direction of propagation. Numerical results for the particular examples of Bi12GeO20(23) and Ba2NaNb5O15(mm2) are also presented.
TL;DR: The structure of UTe2 has been determined by X-ray powder methods as discussed by the authors, and the compound is orthorhombic, space group Immm; a = 4.1617; b = 6.1276; c = 13.965 A.
Abstract: The structure of stoichiometric uranium ditelluride, UTe2, has been determined by X-ray powder methods. The compound is orthorhombic, space group Immm; a = 4.1617; b = 6.1276; c = 13.965 A . Uranium is coordinated by eight tellurium atoms (average distance UTe = 3.17 A ) forming a trigonal prism with two capped, square faces. Half of the tellurium atoms form infinite straight chains with TeTe distances of 3.06 A. β-ErSe2 is probably isostructural with UTe2.
TL;DR: The crystal structure of Me2Sn(NCS)2 has been determined by single crystal X-ray diffraction as discussed by the authors, which consists of rather distorted tetrahedral dimethyltin diisothiocyanate molecules, linked by SSn interactions to form infinite chains along the Z axis with a repeat unit of one molecule.
TL;DR: Inversion to chalcocite (orthorhombic polymorph) at atmospheric pressure and cubic polymorph at 420 degrees C (at atmospheric pressure) were reported in this paper.
Abstract: Inversion to chalcocite (orthorhombic polymorph) at atmospheric pressure, chalcocite inversion to hexagonal polymorph at 103.5 degrees C and cubic polymorph at 420 degrees C (at atmospheric pressure)
TL;DR: In this article, X-ray powder diffraction data have been used to show that realgar synthesized directly from arsenic and sulfur exists in the high temperature β phase, which is metastable at room temperature, and the observed stability of β realgar relative to decomposition to As2S3 was greater than that reported in the literature for α realgar.
TL;DR: In this paper, the influence of ordering on the structure of copper-base martensites has been studied and the ordering, occurring during quenching in the prior β-phase is responsible for the orthorhombic distortion.
TL;DR: In this article, the transformation from ordered γ-phase to ordered e-phase is discussed in terms of the phenomenological theory, and this is related to a mechanism involving a simple lattice shear combined with a shuffle of atoms.
TL;DR: In this paper, the crystal structure of the monopyridine complex of NN′-ethylenebis(salicylideneiminato)cobalt(II), [Co(salen)-(py)], has been determined by a three-dimensional X-ray analysis.
Abstract: The crystal structure of the monopyridine complex of NN′-ethylenebis(salicylideneiminato)cobalt(II), [Co(salen)-(py)], has been determined by a three-dimensional X-ray analysis. The crystals are orthorhombic, space group Cmc21, with a= 20·22, b= 12·44, c= 7·23 A, Z= 4. The structure was solved by the heavy-atom method and refined by the anisotropic least-squares method to an R of 0·071 using 539 independent reflexions. The crystals consist of [Co(salen)(py)] molecules in which the cobalt atom has a pyramidal co-ordination polyhedron. The apical position is occupied by a pyridine molecule parallel to the CH2–CH2 bond. The two chemically equivalent halves of the ‘salen’ ligand and half of the pyridine molecule are related by a crystallographic mirror plane. The inactivity of this compound towards oxygen absorption in the solid state is discussed on the basis of the crystal packing.