Showing papers on "Tetragonal crystal system published in 1977"
TL;DR: In this paper, the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria.
Abstract: It is shown that the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria. Such sintered body containing the metastable phase undergoes stress-induced phase transformation by the absorption of thermal or mechanical stress and exhibits strengths in excess of 690 MPa (100ksi).
387 citations
TL;DR: In this paper, the temperature dependence of the phonon and electron contribution to the dielectric constant, e.g., in the c-and α-axes, was determined and compared to the capacitance measurements.
Abstract: Measurements of all A1 and E transverse and longitudinal phonons in BaTiO3 are reported in the temperature range 10 to 132 °C where the crystal is in the tetragonal phase. A least squares fitting of the spectral shapes is done and the resulting temperature dependence of the frequencies, linewidths and coupling parameters is presented. The temperature dependence of the phonon and electron contribution to the dielectric constant, e, in the c- and α-axes is determined and compared to the capacitance measurements. It is found that the dielectric constant discrepancy is highly anisotropic.
291 citations
TL;DR: In this paper, the structure and properties of piezoelectric materials of composition Pb(ZrxTi1−x)O3 near the morphotropic phase boundary between tetragonal and rhombohedral phases are studied.
244 citations
214 citations
150 citations
TL;DR: In this article, the Raman spectra of ZrO/sub 2/ were measured in the range 300 to 1600/sup 0/K. The temperature dependence of the spectra shows a hysteresis.
Abstract: Raman spectra of ZrO/sub 2/ were measured in the range 300 to 1600/sup 0/K. Irreducible components of the Raman spectra were obtained from polarization measurements at room temperature, and the symmetries of the Raman-active modes in the monoclinic phase were determined. The temperature dependence of the spectra shows a hysteresis. In the temperature range of phase change, two kinds of Raman lines coexist. Six Raman-active mode frequencies were found in the tetragonal phase at high temperatures. Analysis of the spectra showed that the Raman-active modes in the tetragonal phase are affected by strain introduced into the crystals during the phase transformation.
148 citations
TL;DR: In this paper, the system zirconia-scandia was investigated using X-ray diffraction analysis, differential thermal analysis, metallographic analysis, and melting point studies.
Abstract: The system zirconia-scandia was investigated using X-ray diffraction analysis, differential thermal analysis, metallographic analysis, and melting point studies. Results reveal the monoclinic α1 phase (0 to 2 mol% Sc2O3), the tetragonal α2’phase (5 to 8% Sc2O3), the rhombohedral β phase (9 to 13% Sc2O3), the rhombohedral γ phase (15 to 23% Sc2O3), the rhombohedral δ phase (24 to 40% Sc2O3), and the cubic % phase (77.5 to 100% Sc2O3). The monoclinic α1 phase and the tetragonal α2’phase were found to transform to the tetragonal α2 phase over a wide temperature range depending on composition. The β, γ, and α phases transformed to a cubic phase at temperatures of %600%, 1100%, and 1300%C, respectively. A maximum melting point of %2870%C was found at %10% Sc2O3 and a eutectic at %2400%C at 55% Sc2O3.
126 citations
TL;DR: In this article, a series of solid solutions of composition La2−xSrxNiO4 (0 ⩽ x⩽ 1) in which the oxidation state of nickel varies from +2 at 0 to +3 at 0.5 has been prepared.
86 citations
TL;DR: In this article, the magnetoelastic properties of the ferromagnetic cubic compounds of heavy rare earths with zinc ($R\mathrm{Zn}$) are investigated.
Abstract: The magnetoelastic properties of the ferromagnetic cubic compounds of heavy rare earths with zinc ($R\mathrm{Zn}$) are investigated. Lattice distortions occuring below the ordering point are particularly strong when tetragonal: For instance, DyZn exhibits at low temperature a spontaneous tetragonal strain expressed as $\frac{c}{a}\ensuremath{-}1=+8.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. All of these magnetoelastic properties are chiefly due to the crystalline electric field splitting of the ground-state $J$ multiplet. But the tetragonal distortion observed in GdZn below the ordering point reveals pseudodipolar magnetoelastic effects to be important also; this contribution is taken into account for all the compounds. From our strain gauges and capacitance dilatometer experiments we deduce the one-ion and two-ion magnetoelastic coefficients across the series. The former ones are compared with determinations from ultrasonic measurements and their variation through the series is interpreted in terms of crystal-field theory. Finally, an attempt was made to connect these coefficients to the present knowledge of the conduction band in these CsCl-type intermetallic compounds.
80 citations
TL;DR: In this article, the atomic positions of the LuRu4B4 compound were determined through a structural study of the compound and the results were discussed with reference to the previously reported primitive tetragonal MRh4b4 system of superconducting or ferromagnetic compounds.
79 citations
TL;DR: In this article, the electrostatic interaction between a dislocation and an impurity cation-cation vacancy complex is calculated and found to be too small to explain the observed solution hardening rates in the alkali halides, MgO, and Al 2 O 3.
TL;DR: In this paper, the authors showed that the compositional fluctuation wave contained domains of tetragonal or orthorhombic symmetry at a very early stage and the range of order was found to increase during decomposition.
Abstract: Samples in the composition range Fe0.95O-Fe0.88O quenched from about 1000°C, have been studied by electron diffraction/microscopy with special emphasis on the dark-field technique. The set of morphologies obtained by quenching and annealing confirms a spinodal-like decomposition in an oxygen-rich and an almost stoichiometric component. The diffraction spots and dark-field images reveal a considerable degree of order which is enhanced upon heat treatment below 300°C. Previous diffraction studies have been interpreted in terms of an ordered phase with cubic symmetry. Dark-field microscopy, particularly at the symmetric composition, showed that the compositional fluctuation wave contained domains of tetragonal or orthorhombic symmetry at a very early stage. The range of order was found to increase during decomposition. An ordered phase of orthorhombic symmetry developed in oxygen-rich samples. Superstructure spots could be indexed by an A-faced orthorhombic cell with dimensions five times the fundamental cell. Extinctions lead to the space group Abm2 and a periodic antiphase relation. Only four types of clusters, all of which are based on three connected defect tetrahedra, are then possible.
TL;DR: The molecular and crystal structure of squaric acid (3,4−dihydroxy−3,cyclobutene•1,2−dione) has been determined by neutron diffraction techniques at 121°C, a temperature above that of the monoclinic to tetragonal phase transition (∼100°C) as mentioned in this paper.
Abstract: The molecular and crystal structure of squaric acid (3,4‐dihydroxy‐3‐cyclobutene‐1,2‐dione) has been determined by neutron diffraction techniques at 121°C, a temperature above that of the monoclinic to tetragonal phase transition (∼100°C). The high‐temperature structure is in space group I4/m, a=c=6.137(2) A, b=5.337(2) A. Least‐squares refinement has been carried out with 25 variable parameters and 276 reflections, to yield an unweighted R value (on F2) of 0.042. The squaric acid molecule has point symmetry 4/m, and the hydrogen atom is ’’disordered’’ about the inversion center at the midpoint of the O⋅⋅⋅O hydrogen bond. Hydrogen‐bonding parameters are O–H 1.014(4), H⋅⋅⋅O 1.536(5) A, O⋅⋅⋅O 2.548(2) A, & O–H⋅⋅⋅O 176.2(6) °. The tetragonal structure corresponds closely to that obtained from the atomic parameters determined in the monoclinic phase at 25°C, by averaging over the pseudofourfold symmetry.
TL;DR: In this paper, a neutron-scattering study of the ferroelectric transition in CsD/sub 2/PO/sub 4/ has yielded quasi-elastic diffuse distributions of intensity typical of a one-dimensional system with chain-like ordering parallel to the b axis of this monoclinic crystal.
Abstract: A neutron-scattering study of the ferroelectric transition in CsD/sub 2/PO/sub 4/ has yielded quasi-elastic diffuse distributions of intensity typical of a one-dimensional system with chainlike ordering parallel to the ferroelectric b axis of this monoclinic crystal. Therefore, despite such suggestive similarities as the large isotope shift in T/sub c/, the transition is quite different from that of tetragonal KD/sub 2/PO/sub 4/ where the diffuse scattering clearly exhibits characteristics of three-dimensional dipolar interactions.
TL;DR: In this paper, vanadyl doped ZnSO4⋅7H2O was analyzed using a spin-Hamiltonian corresponding to tetragonal symmetry and two bands were observed in the visible region which were attributed to d-d transitions.
Abstract: EPR studies of vanadyl doped ZnSO4⋅7H2O are reported. Vanadyl is found to have fixed orientations in the lattice and there are two magnetically inequivalent complexes in the lattice. The angular variation of the spectra is studied in the crystallographic ab, bc, and ac planes. The principal values of g and A and the direction cosines which the principal axes make with the crystallographic axes are found. Vanadium enters the lattice substitutionally in the place of Zn2+ and gets bonded to five water molecules of the lattice to form a stable [VO(H2O)5]2+ complex. The results obtained from the EPR studies of the polycrystalline samples of vanadyl doped Mg(NH4)2(SO4)2 ⋅6H2O, K2SO4, and 3CdSO4⋅8H2O are also reported. The spectra are analyzed using a spin‐Hamiltonian corresponding to tetragonal symmetry. In the optical absorption spectrum of vanadyl doped ZnSO4⋅7H2O two bands are observed in the visible region which are attributed to d–d transitions. The EPR results in conjunction with the optical results give ...
TL;DR: The crystal structure of V 0.985 Al 0.015 O 2 has been refined from single-crystal X-ray data at four temperatures as mentioned in this paper, and at 373°K it has the tetragonal rutile structure.
TL;DR: In this article, the Czochralski method was used to grow large single crystals of NdNbO4 and NdNBO4, up to 20 mm diameter and 120 mm long, with twinning boundaries of (102) and (201).
TL;DR: In this paper, the crystal structure of α-AlB12 (tetragonal; a = 10.158(2) A, c = 14.270(5) A), space group P41212 or P43212) has been determined by the single-crystal X-ray diffraction method.
TL;DR: In this article, the transformation of near-surface material on grinding and polishing has been investigated in sintered zirconia of 1 μm grain size and 99 % density containing 4.5 and 7.0 mol % Y 2 O 3.
TL;DR: In this paper, the fracture surface energy was determined using the double cantilever beam (DCB) technique and crack lengths were determined by compliance calibration, and the fracture strength was measured in 3-point bending, independent of the thermal treatments.
Abstract: Zirconium oxide-zirconium 2-phase alloys with composition 40 at.% Zr-60 at.% O (23 vol% metal phase) were prepared by hot-pressing mixtures of the oxide and the metal powders. The microstructure consisted of oxide grains completely surrounded by the metal phase. The effective fracture surface energy, γeff, was determined using the double cantilever beam (DCB) technique and crack lengths were determined by compliance calibration. Rapidly cooled specimens, in which the tetragonal to monoclinic phase transition would cause residual stresses, exhibited γeff values as much as 70% greater than stress-relieved specimens (65 J/m2 and 38 J/m2, respectively). A shift in the tetragonal ⇋ monoclinic transition temperature in the as-hot-pressed and the rapidly cooled specimens, compared to the stress-relieved specimens, confirmed the existence of residual stresses. The fracture strength, σeff, measured in 3-point bending, was found to be independent of the thermal treatments. Scanning electron microscopy and optical microscopy revealed that the fracture is transgranular.
TL;DR: In this article, the total energy of metallic hydrogen for a family of face-centered tetragonal lattices carried out within the self-consistent phonon approximation was calculated, showing that the energy of proton motion is large and proper inclusion of the proton dynamics alters the structural dependence of the overall energy, causing isotropic lattices to become favored.
Abstract: A calculation is presented of the total energy of metallic hydrogen for a family of face-centered tetragonal lattices carried out within the self-consistent phonon approximation. The energy of proton motion is large and proper inclusion of proton dynamics alters the structural dependence of the total energy, causing isotropic lattices to become favored. For the dynamic lattice the structural dependence of terms of third and higher order in the electron-proton interaction is greatly reduced from static lattice equivalents.
TL;DR: In this article, the crystal and internal structures of the non-stoichiometric compound TiNx (x = 0.61~0.999, δ-phase, NaCl type) have been studied by electron diffraction and microscopy.
Abstract: The crystal and internal structures of the non-stoichiometric compound TiNx (x = 0.61~0.999, δ-phase, NaCl type) have been studied by electron diffraction and microscopy. In general, interstitial N atoms produce only short-range order, but in TiN0.61 there is long-range order after aging at 500°C for one or three months. The ordered structure is tetragonal with lattice parameters a = 4.198 A 2a0 (a0 = 4.221 A: lattice parameter of disordered TiN0.61), and belongs to the space group I41/amd with the atom positions 8 Ti at 8(e) with z = ¼+0.018, 4 N at 4(a) and 0.88 N at 4(b). The ordered regions develop from small isolated regions and coalesce gradually with aging. The resulting structure contains antiphase and semi-antiphase domain boundaries with respect to the N atom arrangement. The appearance of the semi-antiphase domain boundaries is due to the structure being able to have both 41 and 43 screw axes. The structural difference between TiNx and γ (or ∊)-Ti2N is also discussed.
TL;DR: In this article, a new allotropic phase of a tetragonal body-centered lattice with two atoms per unit cell was found to exist at pressures higher than 121 kbar, and powder patterns corresponding to α' phase were obtained using Bridgman anvils as well as a cubic press.
Abstract: High pressure forms of Ce were studied by means of a Guinier type X-ray diffraction apparatus using Bridgman anvils and boron-epoxy medium. A new allotropic phase of a tetragonal body-centered lattice with two atoms per unit cell was found to exist at pressures higher than 121 kbar. Above 51 kbar, powder patterns corresponding to α' phase were obtained using Bridgman anvils as well as a cubic press, but the crystalline structure could not be determined.
TL;DR: X-ray diffraction studies of EuM2X2 compounds revealed that these compounds crystallize in the ThCr2Si2 type body-centered tetragonal structure, with the space group I4 mmm.
TL;DR: In this article, the concentration dependence of the cubic to tetragonal phase transformation of the CeAgxIn1-x intermetallics is investigated in the silver-rich concentration range by means of resistivity measurements.
Abstract: The concentration dependence of the cubic to tetragonal phase transformation of the CeAgxIn1-x intermetallics is investigated in the silver-rich concentration range by means of resistivity measurements. The measurements show that the concentration dependence of the transition temperatures follows strictly the predictions of the Jahn-Teller-like band model as long as the transition temperatures are above 15K. For the compounds having very low indium contents and for CeAg, another type of phase transformation at about 15K is indicated by the resistivity measurements. The magnetic ordering of the compounds investigated causes a resistivity hysteresis. The magnetic ordering of the compounds investigated causes a resistivity hysteresis. The magnetic ordering temperature, which is about 6K for CeAg, increases with the indium content and supports the assumption that the 4f conduction electron exchange is enhanced by the Fermi energy entering a high density of states peak originating from narrow d type electron bands.
TL;DR: In this article, the formation and stability of tetragonal ZrO 2 powders are closely related to its particle size, and it was found that there is a critical particle size below which the TZO 2 is stable thermodynamically.
TL;DR: In this paper, the authors apply the phenomenological theory of martensitic transformations to the precipitation of β vanadium hydride from b.c. solutions of hydrogen in vanadium.
TL;DR: In this paper, the X-ray photoemission spectra of the band structures of WO3, crystalline HxWO3 and the tetragonal and cubic bronzes were analyzed.
Abstract: X-ray photoemission spectra of the band structures of WO3, crystalline HxWO3 and the tetragonal and cubic bronzes MxWO3 (M=Li, Na) exhibit great similarity. In the bronzes tungsten 5d conduction band states are occupied. The tungsten 4f core level spectra of these materials have an unusual, but characteristic structure attributed to a combination of final state screening and hydrogen or alkali ion neighbor effects. The band structure of amorphous electrochromic WO3 films differs in characteristic ways from that of the crystalline bronzes.