Showing papers on "Tetragonal crystal system published in 1971"
TL;DR: In this article, the infrared and Raman frequencies of monoclinic zirconia and stabilized and metastable tetragonal and cubic cubic Zirconias were established, and the effects of heating, grinding and adding stabilizing oxides on the ir spectra were determined.
Abstract: The infrared and Raman frequencies of monoclinic zirconia and of stabilized and metastable tetragonal and cubic zirconias were established. Infrared spectra were examined by the powder transmission (CsI pellet) and surface reflection techniques. The effects of heating, grinding, and adding stabilizing oxides on the ir spectra were determined. The spectra develop additional bands as the crystal symmetry is lowered, and certain of these bands are highly sensitive to strain-induced distortions of the crystal lattice. Practical applications of ir and Raman spectroscopy to zirconia technology are discussed.
420 citations
181 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 article, the crystal structure of tantalum nitrides was examined by X-ray and electron diffraction techniques and the following seven phases were identified: TaN~0.05 (cubic, β-phase), Ta2N (hexagonal, γ-phase, δ-TaN(hexagonal), e-TaNs (hexagon), Ta5N6, Ta4N5, and Ta3N5 (tetragonal or monoclinic).
Abstract: The crystal structure of tantalum nitrides is examined by X-ray and electron diffraction techniques and the following seven phases are identified: TaN~0.05 (cubic, β-phase), Ta2N (hexagonal, γ-phase), δ-TaN (hexagonal), e-TaN (hexagonal), Ta5N6 (hexagonal), Ta4N5 (tetragonal) and Ta3N5 (tetragonal or monoclinic). Thin films of Ta nitrides for electron diffraction study were prepared by nitriding thin evaporated films of tantalum in ammonia and nitrogen. By heating thin films of Ta3N5 in vacuum, the phase transformations occur successively as follows: Ta3N5→Ta4N5→Ta5N6→e-TaN→Ta2N. The stucture of each nitride form is discussed.
145 citations
141 citations
TL;DR: In this article, the phase transformations in Zn2SiO4 and ZnSiO3 have been investigated at high pressure up to 170 kbar and temperature to 1500°C.
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
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TL;DR: Several transition-metal oxides with formula MxTOm exhibit a wide phase field and high electrical conductivity as mentioned in this paper, and are known as tungsten bronzes, in which the donor m cations occupy tunnels of square, pentagonal, or hexagonal crosssection within a WO3 network of corner-shared octahedra.
90 citations
TL;DR: In this article, a recurrence relation was derived for the square lattice Green's function along the diagonal direction from a couple of the elliptic integrals of the first and second kind, by an elementary partial integration.
Abstract: A recurrence relation, which gives the values of the lattice Green's function along the diagonal direction from a couple of the elliptic integrals of the first and second kind, is derived for the square lattice by an elementary partial integration. The values of the square lattice Green's function at an arbitrary site are then calculated in a successive way with the aid of the difference equation defining the function. Discussions are given of the application of this result to the calculation of the lattice Green's function of the tetragonal and body‐centered cubic lattices.
88 citations
TL;DR: The structure of the high temperature form of Ta2O5 can be stabilized by doping with 2 mole % Sc2O3 and single crystals have been prepared from a Ta 2O5Sc 2O3 (98:2) composition by the Czochralski technique.
80 citations
TL;DR: In this paper, the electrooptic half-wave field distance product of Cd [Hg (SCN)4] single crystals, belonging to the tetragonal crystal class I 4, has been measured.
TL;DR: The real and imaginary parts of the lattice Green's functions for the simple cubic (actually the tetragonal), body-centered cubic, and facecentered cubic lattices, at the variable from −∞ to +∞, are expressed as a sum of simple integrals of the complete elliptic integral of the first kind as discussed by the authors.
Abstract: The real and imaginary parts of the lattice Green's functions for the simple cubic (actually the tetragonal), body‐centered cubic, and face‐centered cubic lattices, at the variable from −∞ to +∞, are expressed as a sum of simple integrals of the complete elliptic integral of the first kind. The results of the numerical calculations obtained with the aid of the formulas are shown by graphs.
TL;DR: In this article, the anomalous specific heat of Mn-Zn, Mn-Ga and Mn-Ge alloys was investigated with X-ray and neutron diffraction and specific heat measurements.
Abstract: Manganese-rich γ-phase alloys of Mn-Ni, Mn-Zn, Mn-Ga and Mn-Ge have been investigated with X-ray and neutron diffraction and specific heat measurements. The Mn-Zn, Mn-Ga and Mn-Ge alloys exhibit antiferromagnetism below the transition temperature, at which the cubic lattice is transformed to the tetragonal lattice (the axial ratio c / a 1) at a lower temperature. The magnetic structure for the axial ratio c / a >1 is different from that for the axial ratio c / a <1. The integrated values of the anomalous specific heat are less than the values predicted by the localized moment model of antiferromagnetism.
TL;DR: The crystal structure of acetyl-L-proline-N-methylamide has been determined by the symbolic addition method as discussed by the authors, where the molecules are bound together through N H.. O hydrogen bonds to form a chain about the twofold screw axis parallel to c.
Abstract: The crystal structure of acetyl-L-proline-N-methylamide has been determined by the symbolic addition method. The crystal is orthorhombic, space group P21212x with four molecules in a cell of dimensions a = 9.74_+ 0.01, b = 13.20 +__ 0.01, c = 7.17 _+ 0.01/~. Refinement was carried out by the full-matrix leastsquares method including anisotropic thermal parameters. The final R value for 1213 reflexions was 0.098. The main chain of the molecule containing two trans planar peptide groups takes a folded conformation, the dihedral angle between the two peptide planes being 69.4 °. The two imino nitrogen atoms are arranged nearly in cis position and the torsion angles, tp and g are 103.7 and 164.2 ° respectively, indicating that the conformation is fairly close to that of the right-handed e-helix. The molecules are bound together through N H . . . O hydrogen bonds to form a chain about the twofold screw axis parallel to c.
TL;DR: In this paper, three phases with related structures are made in evidence at any composition; they are respectively monoclinic, orthorhombic and tetragonal with the rutile structure.
TL;DR: In this article, two new phases of niobium nitride, Nb4N5 and Nb5gN6, were identified on thin films by electron diffraction.
Abstract: Two new phases of niobium nitride, Nb4N5 and Nb5gN6, were identified on thin films by electron diffraction. The specimens were prepared by nitriding the evaporated thin films of niobium in ammonia. The structures of these two nitrides are isomorphous with those of Ta4N5 and Ta5N6, respectively. The Nb4N5 phase belongs to the tetragonal system with lattice parameters, a = 6.87 3 A and c = 4.29 8 A , while the Nb5N6 phase is based on the hexagonal structure having lattice parameters, a = 5.19 3 A and c = 10.38 0 A . By heating Nb5N6 in vacuum at high temperature, successive phase changes were observed: Nb5N6→δ′-NbN→δ-NbN→Nb4N3→Nb2N.
TL;DR: In this article, the experimental data are interpreted in terms of two cation migration processes, namely the cation exchange between the octahedral and tetrahedral sublattices, and an octagonal Mn 3+ clustering.
TL;DR: A study of the chemical properties, character of the thermal decomposition, and the IR spectra makes it possible to characterize magnesium borohydride as being a pure compound as discussed by the authors.
Abstract: 1
A study of the chemical properties, character of the thermal decomposition, and the IR spectra makes it possible to characterize magnesium borohydride as being a pure compound
2
Magnesium borohydride exists in two crystalline modifications:α-Mg(BH4)2 has a tetragonal lattice (a=1359, c=1651 A), whileβ-Mg(BH4)2 has a cubic face-centered lattice (a=155 A) The temperature of the polymorphic transition is 186° The density of theα-modification is 0989 g/cm3
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Based on a combination of the studied properties and the degree of covalency, magnesium borohydride finds itself between lithium and beryllium borohydrides
TL;DR: The crystal structure of the intermetallic phase GdAg3.6 has been determined using three-dimensional diffractometer data from three different crystals as mentioned in this paper, with lattice parameters a= 12.670 and c= 9-332/~.
Abstract: The crystal structure of the intermetallic phase GdAg3.6 has been determined using three-dimensional diffractometer data from three different crystals. The space group is P6/m, with lattice parameters a= 12.670 and c= 9-332/~. One disordered silver set is partially occupied. The range of stoichiometry of the phase is thought to be quite limited, corresponding to approximately 50% occupancy of the disordered set (X-ray density= 9.86 g.cm-3). On the basis of the very close correlation of the lattice parameters, this phase, common to many of the rare-earth-silver systems, likely defines the structure of the previously reported phase PuAg3.
TL;DR: In this paper, the Schottky barrier at the film-electrode interface was used to detect switchable spontaneous polarization values as high as 20% of the bulk single crystal value.
Abstract: Flash evaporated, ferroelectric, barium titanate films have been prepared in the thickness range 0.04-2.0 mu m. They consist of oriental tetragonal crystallites having dimensions comparable with film thickness. Thickness dependent permittivity and other dielectric properties are interpreted in terms of Schottky barriers at the film-electrode interface. Switching is observed in films as thin as 0.08 mu m and loops and current transients are surprisingly similar to those from bulk ceramics. Switchable spontaneous polarization values are as high as 20% of the bulk single crystal value.
IBM1
TL;DR: Most of the vibrational modes have been measured in the tetragonal ferroelectric phase of Pb 1−x Ba x TiO 3 for 0 3 ⪕ x ⫕ 1 using the powder Raman technique as mentioned in this paper.
01 Aug 1971-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the authors have made measurements on highly tetragonal bct martensite in two Fe−Al−C steels and the results have been interpreted in terms of the phenomenological crystallographic theory of Martensite formation.
Abstract: Crystallographic measurements on highly tetragonal bct martensite in two Fe−Al−C steels have been made and the results have been interpreted in terms of the phenomenological crystallographic theory of martensite formation. Agreement between theory and experiment was found to be excellent. Of particular interest is the high martensite tetragonality (c/a→1.14) in aluminum-steels compared to others. Because of this the principal distortions of the Bain deformation are substantially smaller and consequently the magnitudes of the shape and lattice invariant deformations are reduced considerably. Measurements of the dilatation parameter δ indicate that the shape deformation is not significantly different from an invariant plane strain.