Showing papers on "Tetragonal crystal system published in 1979"
TL;DR: In this paper, a tetragonal crystal field splitting of both the 4f1 ground state and 5d1 excited states of YAG:Ce3+ in YAG has been investigated.
Abstract: Absorption and luminescence spectra of YAG:Ce3+ crystals have been measured at various temperatures between 4.2° and 300°K. The high resolution, low temperature spectra show resolved fine structure. Zero‐phonon transitions have been assigned and the phonon replicas correlated with lattice phonon energies. The characteristic absorption band of YAG:Ce3+ near 460 nm decreases in intensity, whereas that near 340 nm increases with increasing temperature. This effect is explained in terms of a tetragonal crystal field splitting of both the 4f1 ground state and 5d1 excited states of Ce3+ in YAG. When allowance is made for changes in the absorption of pump light with temperature the photoluminescence quantum efficiency of Ce3+ in YAG is constant up to 300°K. The significance of these crystal field effects for the use of YAG:Ce as a high temperature lamp phosphor is discussed.
172 citations
TL;DR: Although this analysis at a single temperature cannot establish whether thermal motion or static disorder (including conformational variability) underlies the observed effects, it suggests that the accurate determination of temperature factors will be useful in detailed studies of the dynamic properties of macromolecules.
144 citations
TL;DR: In this article, integrated X-ray intensities of Bragg peaks were observed from single crystals of Zr0.866Ca0.134Ol and Zr 0.786Y0.214O1.
Abstract: Integrated X-ray intensities of Bragg peaks were observed from single crystals of Zr0.866Ca0.134Ol.866 and Zr0.786Y0.214O1.893 in the disordered state. There are displacements of oxygen ions (characterized by Δ/a ~ 0.05) from the ideal positions of the fluorite structure along (100) directions similar to those that occur on ordering below 1273 K and related to the cubic to tetragonal transition in pure ZrO2. These displacements are not related to anharmonicity, at least to fourth-order terms. In addition, there are small displacements of the cations (Δ/a ~ 0.015) in (111) directions in the yttria-stabilized zirconia.
101 citations
TL;DR: In this paper, electron microscopy has been used to study silicon and germanium particles prepared by evaporation in argon at low pressure and showed frequently distinct crystal habits.
99 citations
TL;DR: In this paper, the β-tetragonal (or tetragonal II or III) boron modification has been obtained from single crystals of the so-called β-Tetragonal BORON modification, which were obtained by hydrogen reduction of BBr3 on tantalum filament at 1200°C.
84 citations
TL;DR: In this paper, the experimental spectra of the uranyl ion, in tetragonal and trigonal equatorial fields, were compared with an empirical model of the excited states arising from four possible configurations of the...
Abstract: The experimental spectra of the uranyl ion, in tetragonal and trigonal equatorial fields, are compared with an empirical model of the excited states arising from four possible configurations of the...
77 citations
TL;DR: In this paper, a study of the fluorite structure stoichiometric TiH 2 by means of the augmented plane wave method reveals that the density of states at the Fermi level is very high, due mainly to a degenerate flat band in the Λ L direction.
76 citations
TL;DR: In this paper, the phase diagram of thermally depoled tetragonal PLZT materials has been investigated by means of X-ray diffraction, Capacitance and DSC measurements.
74 citations
TL;DR: In this article, a latent heat effect is observed at the sharp FEt → PEc transition in PLZT x/30/70 materials with a low La content (x <16 at° La).
65 citations
TL;DR: In this article, the transformation between two polymorphs of CaSi2 has been studied at equilibrium and nonequilibrium conditions at high pressure-high temperature conditions under both equilibrium and non-equilibrium conditions.
56 citations
TL;DR: In this article, the lattice parameters and crystal field splitting of the uppermost valence band in CuGaS2 are measured as a function of temperature, and the linear thermal expansion coefficients along the "a" and "c" axes are estimated to be 11.2×10-6 and 4.1 × 10-6 respectively.
Abstract: The lattice parameters and crystal field splitting of the uppermost valence band in CuGaS2 are measured as a function of temperature. The linear thermal expansion coefficients along the "a" and "c" axes are estimated to be 11.2×10-6 and 4.1×10-6 respectively, and the axial ratio, c/a, changes with a coefficient of -9.0×10-6. This result indicates an "increase" in tetragonal distortion, (2-c/a), with temperature, and hence, an increase in crystal field splitting is expected. However, the apparent crystal field splitting shows a slight "decrease" with temperature. An attempt to explain this contradictory feature is discussed using the concept of the p-d hybridization effect on crystal field splitting.
TL;DR: Five new oxidpnictides have been prepared and structurally characterized, and Mn- and As(Sb,Bi) atoms form tetragonal pyramids, connected by common edges in the basis to two-dimensional sheets.
Abstract: Five new oxidpnictides have been prepared and structurally characterized. They crystallize in the tetragonal system, I4/mmm, with the following constants: Sr₂Mn₃As₂O₂: a = 416 ± 1 pm, c = 1884 ± 4 pm, c/a = 4.529, Ba₂Mn₃As₂O₂ : a = 424.8 ± 0 5 pm, c = 1977 ± 3 pm, c/a = 4.654, Sr₂Mn₃Sb₂O₂ : a = 426.2 ± 0.4 pm, c = 2011 ± 2 pm, c/a = 4.718, Ba₂Mn₃Sb₂O₂ : a = 436.7 ± 0.5 pm, c = 2078 ± 2 pm, c/a = 4.758, Sr₂Mn₃Bi₂O₂ : a = 428 ± 1 pm, c = 2055 ± 5 pm, c/a = 4.801. Mn- and As(Sb,Bi) atoms form tetragonal pyramids, connected by common edges in the basis to two-dimensional sheets. These sheets are separated by double layers of Sr atoms, in which Mn and O atoms are located forming MnO₄ square plane nets.
TL;DR: In this article, the authors used Fermi-surface pressure-derivative measurements at 2 K and single-crystal and powder x-ray studies as a function of pressure at room temperature to demonstrate that recently published anomalous surface and lattice properties of ReO/sub 3/ are related to a novel second-order phase transition.
Abstract: We have used Fermi-surface pressure-derivative measurements at 2 K and single-crystal and powder x-ray studies as a function of pressure at room temperature to demonstrate that recently published anomalous Fermi-surface and lattice properties of ReO/sub 3/ are related to a novel second-order phase transition. This transition probably involves a tetragonal distortion of the lattice accompanying a displacement of the O atoms from the linear O-Re-O chains of cubic ReO/sub 3/ to a ''hinged'' arrangement of the oxygens and is characterized by an enormous increase in the compressibility of the high-pressure phase.
TL;DR: The first Vanadium-hollandite tunnel sites with univalent cations were reported in this article. But they were obtained by high pressure-high temperature treatment of KVO3 and TlVO3 in a modified Belt-type apparatus.
TL;DR: In this paper, the system CdIn 2 S 4− x Se x is investigated by means of X-ray diffraction, and three phases present in the system: (i) a cubic spinel phase for x = 0 to x = 1.25, (ii) a rhombohedral phase of ZnIn 2S 4−x Se x type, and (iii) a tetragonal thiogallate phase for X = 3.5 to x=4.0.
01 Jan 1979
TL;DR: In this article, the Wigner-Eckart theorem is used for point groups of Tensor Operators in the Ligand Field to calculate the average effective magnetic moment as a function of temperature and Dq.
Abstract: I.- 1. Introduction.- 2. Conventional Magnetism Diagrams and Their Limitations. Present State of the Art.- 3. Tensor Operator Algebra for Point Groups.- 3.1. Tensor Operators and the Wigner-Eckart Theorem.- 3.2. 3-? and 6-? Symbols.- 3.3. Tensor Operators in Subgroups of SO(3).- 3.4. Kronecker and Scalar Products of Tensor Operators.- 3.5. Tensor Operators of the Ligand Field.- 4. The Weak-Field Method.- 4.1. The Hamiltonian, States, and Wave Functions.- 4.2. The Various Coefficients.- 4.3. Matrix Elements.- 4.4. Calculation of Magnetic Susceptibility.- 5. The Intermediate-Field Method.- 5.1. The Hamiltonian, States, and Wave Functions.- 5.2. The Various Coefficients.- 5.3. Matrix Elements.- 6. Description of Programs.- 6.1. General Outline.- 6.2. Computation of Matrix Elements.- 6.3. Diagonalization of Energy Matrix.- 6.4. Calculation of Magnetic Susceptibility.- 7. Description of the Diagrams and Their Application.- Appendix. The Projection Operators.- References.- II Diagrams.- Average Effective Magnetic Moment as Function of Temperature and Dq, K =1.0.- 1d Electron, Octahedral and Tetrahedral Symmetry.- 1d Electron, Tetragonal Symmetry.- 1d Electron, Trigonal Symmetry.- 1d Electron, Cylindrical Symmetry.- 2d Electrons, Octahedral and Tetrahedral Symmetry.- 2d Electrons, Tetragonal Symmetry.- 2d Electrons, Trigonal Symmetry.- 2d Electrons, Cylindrical Symmetry.- 3d Electrons, Octahedral and Tetrahedral Symmetry.- 3d Electrons, Tetragonal Symmetry.- 3d Electrons, Trigonal Symmetry.- 3d Electrons, Cylindrical Symmetry.- 4d Electrons, Octahedral and Tetrahedral Symmetry.- 4d Electrons, Tetragonal Symmetry.- 4d Electrons Trigonal Symmetry.- 4d Electrons, Cylindrical Symmetry.- 5d Electrons, Octahedral and Tetrahedral Symmetry.- 5d Electrons, Tetragonal Symmetry.- 5d Electrons, Trigonal Symmetry.- 5d Electrons, Cylindrical Symmetry.- 6d Electrons, Octahedral and Tetrahedral Symmetry.- 6d Electrons, Tetragonal Symmetry.- 6d Electrons, Trigonal Symmetry.- 6d Electrons, Cylindrical Symmetry.- 7d Electrons, Octahedral and Tetrahedral Symmetry.- 7d Electrons, Tetragonal Symmetry.- 7d Electrons, Trigonal Symmetry.- 7d Electrons, Cylindrical Symmetry.- 8d Electrons, Octahedral and Tetrahedral Symmetry.- 8d Electrons, Tetragonal Symmetry.- 8d Electrons, Trigonal Symmetry.- 8d Electrons, Cylindrical Symmetry.- 9d Electrons, Octahedral and Tetrahedral Symmetry.- 9d Electrons, Tetragonal Symmetry.- 9d Electrons, Trigonal Symmetry.- 9d Electrons, Cylindrical Symmetry.- Average Effective Magnetic Moment as Function of Temperature and Dq, K = 0.75, 0.50.- 1d Electron, Tetragonal, Trigonal, and Cylindrical Symmetry.- 2d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 3d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 4d Electrons, T etragonal, Trigonal, and Cylindrical Symmetry.- 5d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 6d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 7d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 8d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 9d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- Principal Effective Magnetic Moments as Function of Temperature and Dq.- 1d Electron, Tetragonal, Trigonal, and Cylindrical Symmetry.- 2d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 3d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 4d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 5d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 6d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 7d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 8d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.- 9d Electrons, Tetragonal, Trigonal, and Cylindrical Symmetry.
TL;DR: In this article, the deformation and misorientation of InxGa1−xAs epitaxial layers grown on InP substrates by molecular beam epitaxy is measured from rocking curves of an x-ray doublecrystal monochrometer.
Abstract: Lattice deformation and misorientation of InxGa1−xAs epitaxial layers grown on InP substrates by molecular‐beam epitaxy is measured from rocking curves of an x‐ray double‐crystal monochrometer. It is concluded that the epitaxial layers are deformed from cubic to tetragonal and misoriented to the substrates except in lattice‐matched epilayers. This result suggests that the substrate lattice has a large influence on the structure of the epitaxial layers.
TL;DR: In this article, it was shown that HoRh4B4 is ferromagnetic TC = (6.8±0.2) K with the moment parallel to the unique c tetragonal axis.
Abstract: Our measurements show that HoRh4B4 is ferromagnetic TC= (6.8±0.2) K with the moment parallel to the unique c tetragonal axis. (AIP)
TL;DR: The influence of PbO modification on the formation of 4PbO·PbSO4 paste was determined by X-ray diffraction analysis and scanning electron microscopy as discussed by the authors.
Abstract: The influence of PbO modification on the formation of 4PbO·PbSO4 paste is determined by X-ray diffraction analysis and scanning electron microscopy. The paste was prepared from tetragonal PbO, orthorhombic PbO and several mixtures of both oxides at 80° C and a H2SO4/PbO ratio of 6 wt%.
TL;DR: In this paper, the crystal and molecular structure of Zn3·5O(O2CMe)5(py)2 is determined from diffractometric data by the heavy-atom method and refined by least squares to R 0.076.
Abstract: Crystals of the title complex [{Zn3·5O(O2CMe)5(py)}2](py = pyridine) are orthorhombic, space group Pbca, with unit-cell dimensions a= 16.598(3), b= 14.682(4), c= 19.111(9)A, and Z= 4. The crystal and molecular structure has been determined from diffractometric data by the heavy-atom method and refined by least squares to R 0.076. Seven zinc atoms, bridged by acetate groups, form a heptameric centrosymmetrical unit. In each of the two semi-units a central oxygen is surrounded tetrahedrally by three zinc atoms which are in a tetrahedral arrangement, and by one zinc atom in a tetragonally compressed octahedral environment. The low-temperature e.s.r. spectrum of 63Cu-doped crystals of the complex is reported. The paramagnetic ion is substituted at the compressed tetragonal zinc site. The g, metal hyperfine-coupling, and quadrupole-coupling tensors have been obtained from an analysis of the angular variation of the spectra. In spite of the low site symmetry indicated by the X-ray results, an almost pure dz2 ground state is found to be present. A small 4s admixture is assumed to be responsible for the reduced value of the isotropic part of the copper hyperfine tensor.
TL;DR: In this paper, a new model is proposed to explain the magnetostriction effects in ferrimagnetic spinels and garnets with Mn3+, Co2+, and Fe2+ ions substituted into octahedral sites.
Abstract: A new model is proposed to explain the magnetostriction effects in ferrimagnetic spinels and garnets with Mn3+, Co2+, and Fe2+ ions substituted into octahedral sites. Considerable experimental evidence has revealed that small amounts of each of these ions will alter substantially the magnitude of either the λ100 or λ111 magnetostriction constant, depending on the particular ion. The theory is based on the concept that Jahn‐Teller effects produce local site distortions of tetragonal (favoring 〈100〉 axes) or trigonal (favoring 〈111〉 axes) symmetry which are able to switch among the different axes of the particular family in order to select the axis closest to the direction of the magnetic field. For Mn3+ ions, the local site distortions are expected to be tetragonal (c/a≳1), in accordance with observations in a variety of magnetic oxides where static cooperative effects are present and will produce large positive changes in the λ100 constant. With Co2+ ions the distortion is also tetragonal, but of the oppo...
TL;DR: In this article, the structural relationship between Ni 11 Zr 9 and NiZr is discussed and atomic positions are given and the structural relationships between Ni11 Zr9 and NZr are discussed.
Abstract: Ni 11 Zr 9 has been investigated by X-ray diffraction. This compound crystallizes in the tetragonal I4 m space group. Its lattice parameters are a = 9.88 ± 0.01 A and c = 6.61 ± 0.01 A . Atomic positions are given and the structural relationships between Ni 11 Zr 9 and NiZr are discussed.
TL;DR: In this article, single crystals of tetragonal boron were obtained from bboron deposits prepared by hydrogen reduction of BBr3 on tantalum filaments at 1200 °C.
Abstract: Single crystals of tetragonal boron were obtained from boron deposits prepared by hydrogen reduction of BBr3 on tantalum filaments at 1200 °C. Chemical analysis of the samples showed that this phase can be regarded as a true modification of pure elemental boron. The lattice parameters are a = 10.14(1) A and c = 14.17(1) A . The unit cell contains four chemical units B21·2B12·B2.5 , resulting in dc = 2.343 gcm−3 (dm = 2.360(3) g cm−3). The space group is P41orP43. The structure of this form of boron consists of a three-dimensional boron skeleton built on simple octahedra B12 and twinned icosahedra B21. A number of interstitial sites are totally or partially filled by boron atoms.
TL;DR: The electrical conductivity and thermoelectric power of two forms (tetragonal and orthorhombic) of the new organic conductor (tetraphenyldithiapyranilidene) [φ4DTP)(I-3] have been measured as discussed by the authors.
TL;DR: In this paper, structural and magnetic properties of a number of pseudo-ternaries of the composition Nd(Mn1−xCrx)2Si2 have been examined and the possibility of modifying the nature of magnetic interaction between rare earth and Mn atoms through the incorporation of a second transition metal atom (in this instance Cr) into the lattice was discussed.
Abstract: Structural and magnetic properties of a number of pseudo‐ternaries of the composition Nd(Mn1−xCrx)2Si2 have been examined. In the composition range 0
TL;DR: In this paper, powder patterns of the cubic and orthorhombic phases calculated from the crystal structure data are compared with the observed patterns, and the so-called tetragonal phase is shown by electron diffraction to be orthorHombic, pseudo-tetragonal, and probably has the symmetry Pcaa with a = b = 10.8599
Abstract: Indexed powder diffraction data are presented for Ca3Al2O6 and its sodium-containing solid solutions. Powder patterns of the cubic and orthorhombic phases calculated from the crystal structure data are compared with the observed patterns. Indexed data are presented for the monoclinic phase, which is stabilized by sodium and silicon. The so-called tetragonal phase is shown by electron diffraction to be orthorhombic, pseudo-tetragonal. It probably has the symmetry Pcaa with a = b = 10.8599 (9), c = 15.1234 (20) A.