Showing papers on "Tetragonal crystal system published in 1982"
TL;DR: In this article, the dielectric, piezoelectric and elastic properties of 0.91(PbZn1/3Nb2/3)O3−0.09PbTiO3 single crystals have been investigated as functions of temperature and applied electric field.
Abstract: The dielectric, piezoelectric and elastic properties of 0.91(PbZn1/3Nb2/3)O3–0.09PbTiO3 single crystals have been investigated as functions of temperature and applied electric field. Two multiple phase transitions at 68°C and 178°C, the crystal changing from the rhombohedral ferroelectric phase to tetragonal ferroelectric and then to cubic paraelectric, have been observed. Both the transitions are of first-order, but both are slightly diffused. Significant increases in the dielectric, piezoelectric and elastic constants are observed at the lower transition point. In particular, the sample poled along the pseudo-cubic [001] axis reveals anomalously large piezoelectric and electro-mechanical coupling constants at room temperature in the rhombohedral phase (d[001]//=1500×10-12 C/N, k[001]//=0.92).
900 citations
TL;DR: In this paper, the stability of tetragonal ZrO2 particles in ceramic matrices was considered, with particular reference to Al2O3-ZrO 2 composites and to partially stabilized TZRO 2.
Abstract: The stability of tetragonal ZrO2 particles in ceramic matrices was considered, with particular reference to Al2O3-ZrO2 composites and to partially stabilized ZrO2. In both systems, particles above a “critical” size transform martensitically to monoclinic symmetry on cooling to room temperature. The critical factors that could affect the size dependence of the transformation temperature—surface and strain energy effects, the chemical free energy driving force, and the difficulty of nucleating the martensitic transformation—were considered. Nucleation arguments are probably the most important.
484 citations
TL;DR: YPO4, ScPO4 and LuPO4 crystallize in the tetragonal system conforming to space group model I41/amd (D194h, No. 141), Z = 4.
174 citations
108 citations
TL;DR: In this article, a special technique was developed to obtain perovskite ceramics exhibiting no co-existence in the boundary compositions, in which no compositional fluctuation occurred in the B site of the structure.
Abstract: Tetragonal and rhombohedral phases always coexist in Pb(ZrxTil1−x)03 near the morphotropic phase boundary compositions (0.52≤x≤0.55) when prepared by solid-solid reaction among the constituent oxides. A special technique was developed to obtain perovskite ceramics exhibiting no co-existence in the boundary compositions, in which no compositional fluctuation occurred in the B site of the perovskite structure. Even these monophasic perovskite ceramics of the morphotropic phase boundary compositions were two-phase with the lapse of time after poling. This phenomenon is interpreted in terms of thermodynamics. It is suggested that this phenomenon may closely relate to the origin of aging in piezoelectrics.
105 citations
TL;DR: The phase transformation from the tetragonal to the hexagonal crystal modification in highly oriented lamellae of poly-butene-1 has been followed by transmission electron microscopy (TEM) as discussed by the authors.
Abstract: The phase transformation from the tetragonal to the hexagonal crystal modification in highly oriented lamellae of poly-butene-1 has been followed by transmission electron microscopy (TEM). It is fo...
105 citations
TL;DR: The first complete set of electronic structure calculations for elemental boron in its alpha-rhombohedral (12 atoms per unit cell), beta-RHOMBOME (105 atoms) and suggested alpha-tetragonal (50 atoms) crystalline forms were reported in this paper.
Abstract: The first complete set of electronic structure calculations are reported for elemental boron in its alpha -rhombohedral (12 atoms per unit cell), beta -rhombohedral (105 atoms) and suggested alpha -tetragonal (50 atoms) crystalline forms. The results show that a band picture provides an accurate description of the bonding in these solids. The alpha -rhombohedral structure is found to produce semiconducting properties, with an indirect gap of 1.7 eV. The ordering of bands can be qualitatively interpreted in terms of the internal molecular orbitals of a B12 icosahedron and the two-centre and three-centre external bonds linking neighbouring icosahedra. Replacement of the electron-deficient bonds by linear C3 units gives the much stronger B12C3 structure, in which the calculated gap increases to a direct 3.8 eV. In the more complicated beta -rhombohedral elemental structure, a forbidden gap approximately 2.7 eV occurs in the spectrum of electron states. Some degree of defect- or impurity-induced disorder seems essential to stabilise the structure, since the valence band of the 'ideal' structure can accommodate 320 electrons per unit cell, compared with the 315 available. In the suggested alpha -tetragonal modification of pure boron, the electron deficit would be so severe that this structure probably occurs only for compounds such as B50C2 and B50N2.
93 citations
87 citations
TL;DR: In this article, the cubic rare earth intermetallics compound PrPb3 (AuCu3-type structure) undergoes a transition at 0.35 K: as it is a Van Vleck paramagnet, the low temperature phase was assumed to be quadrupolarly ordered.
85 citations
TL;DR: In this paper, high pressure structural phase transitions of GaAs and GaP have been studied by energy dispersive X-ray diffraction with the radiation from the Cornell High Energy Synchrotron Source.
Abstract: High pressure structural phase transitions of GaAs and GaP have been studied by energy dispersive X-ray diffraction with the radiation from the Cornell High Energy Synchrotron Source. GaAs began to transform at 172 + or - 7 kbar to an orthorhombic structure possibly belonging to space group Fmmm. GaP transformed to a tetragonal beta-Sn type phase at 215 + or - 8 kbar. Although pressure transmitting media were used to minimize shear stresses in the specimens, the high pressure diffraction results were interpreted as showing evidence for planar defects in the specimens.
76 citations
TL;DR: New high-pressure, high-temperature, single-crystal x-ray techniques were used to bracket the reversible monoclinic (ferroelastic) to tetragonal (paraelastic) transition.
Abstract: Lattice dimensions of bismuth vanadate have been determined under 37 different high-pressure or high-temperature conditions or a combination of these conditions. New high-pressure, high-temperature, single-crystal x-ray techniques were used to bracket the reversible monoclinic (ferroelastic) to tetragonal (paraelastic) transition.
TL;DR: In this paper, the magnetic response of a single crystal of the tetragonal compound ErRh/sub 4/B/sub 6/4/1/4 in c-bar and a-bar orientations is presented.
Abstract: The magnetic response of a single crystal of the tetragonal compound ErRh/sub 4/B/sub 4/ in c-bar (hard) and a-bar (easy) directions is presented Great differences are found in the magnetic and superconducting behavior between the two crystallographic orientations This anisotropy naturally separates the bare superconducting properties of ErRh/sub 4/B/sub 4/ from those affected by magnetism Along the a-bar axis evidence is found for a first-order phase transition at H/sub c/2 for T< or approx =3 K Below T/sub c/2 the data reconcile the discrepancy between the measured ferromagnetic moment per erbium atom by neutron scattering and by Moessbauer effect
TL;DR: A structural distortion in the primitive cubic phase of the SnM3Rh4Sn12 compounds with M = La, Ce, Pr, Nd, Sm, and Gd has been detected by electron diffraction and studied by X-ray diffraction as mentioned in this paper.
TL;DR: In this paper, a new type of A5B3-structure based on the L10-type was found in the Al-Ti and Ga-Ti systems; the structure has a tetragonal symmetry with the space group, P4/mbm, and the lattice constants, 2√2af and cf, where af and cf are those of the fundamental L10 type cell.
Abstract: By electron diffraction and X-ray powder diffraction, a new type of A5B3-structure based on the L10-type was found in the Al–Ti and Ga–Ti systems; Al5Ti3 and Ga5Ti3. The structure has a tetragonal symmetry with the space group, P4/mbm, and the lattice constants, 2√2af and cf, where af and cf are those of the fundamental L10-type cell. 20 Al (or Ga) and 12 Ti atoms are contained in the unit cell. The structure can be described as follows: it consists of the domains based on the L12, containing 3×2 columns of Ti atoms, and the domain boundaries have the L10-type atomic arrangement.
TL;DR: In this paper, solid solutions of the formula La2−xLnxCuO4 (Ln = Pr, Nd) possess the orthorhombic structure of La2NiO4 for small values of x and transform to the tetragonal Nd2NiF4 structure at a critical value of x.
TL;DR: In this paper, the elastic constants of two single crystals of the thermally quenched gamma phase (FCC) alloy Fe1-xPdx with x=0.28 and 0.37 were observed to decrease in energy around the Gamma point as the magnetisation increases.
Abstract: Neutron inelastic scattering measurements have been carried out on two single crystals of the thermally quenched gamma phase (FCC) alloy Fe1-xPdx with x=0.28 and 0.37. The x=0.28 sample (crystal 2) exhibits a face centred cubic to face centred tetragonal (FCC-FCT) transition at Tm approximately 265K. The x=0.37 sample (crystal 1) does not undergo a structural transition. For both crystals the ( zeta zeta 0) TA1 phonon branch, which corresponds to the elastic constant (C11-C12)/2, decreases in energy around the Gamma point as the magnetisation increases. The amount of softening of the elastic constant, Delta (C11-C12)/2, of crystal 2 is much larger than that of crystal 1 and has the same temperature dependence as the square of the magnetisation, M(T)2. The temperature dependence of (C11-C12)/2 implies that this phonon softening is the cause of the FCC-FCT transition. The other branches display very little if any anomalous behaviour. A large phonon broadening has been observed in the soft phonon branch. Discussions of the broadening and the results of magnon measurements are also presented.
TL;DR: The cytochrome P-450CAM monooxygenase from Pseudomonas putida has been crystallized in three forms designated orthorhombic I, tetragonal I, and orthorHombic II.
TL;DR: In this article, the activation energy of amorphous Zr1−xCox ribbons was derived from the dependence of Tx on the heating rate and the difference in the concentration dependence of both series of activation energies was ascribed to a temperature-dependent configurational entropy associated with the presence of chemical short-range ordering in the amorphized Zr-Co alloys.
Abstract: Several new metastable Zr-Co phases were observed in a study of the crystallization of amorphous Zr1−xCox ribbons using differential scanning calorimetry and X-ray diffraction. The cubic structure of Zr2Co (Ni2Ti type) transformed into the tetragonal CuAl2 type upon heating. The crystallization temperatures Tx were analysed in terms of a model proposed earlier where the activation energy for crystallization is approximated by the formation enthalpy of a hole the size of a cobalt atom. Experimental values for the activation energy were derived from the dependence of Tx on the heating rate. The difference in the concentration dependence of both series of activation energies was ascribed to a temperature-dependent configurational entropy associated with the presence of chemical short-range ordering in the amorphous Zr-Co alloys.
TL;DR: In this paper, the fracture surfaces of a commercial partially stabilized ZrO2 that had undergone subcritical crack growth in H20 were characterized by scanning and transmission electron microscopy.
Abstract: Fracture surfaces of a commercial partially stabilized ZrO2 that had undergone subcritical crack growth in H20 were characterized by scanning and transmission electron microscopy. At high stress intensities (≥4.6 MPa·m−1/2), fracture was primarily trans granular, and coherent tetragonal ZrO2 precipitates had undergone a martensitic transformation to monoclinic symmetry. At lower stress intensities, where power-law crack growth occurred, fracture suflaces were primarily inter-granular, and the tetragonal ZrO2 had transformed to a new ZrO2 polymorph with orthorhombic symmetry.
TL;DR: In this article, it is shown that the doubling of one of the perovskite cell axes appears at random in the a, b or c directions within the same crystal.
TL;DR: Tetragonal and cubic CuFe2O4 are prepared and studied by Mossbauer effect technique at room temperature and at 4.2 K with and without applied strong magnetic fields as mentioned in this paper.
Abstract: Tetragonal and cubic CuFe2O4 are prepared and studied by Mossbauer-effect technique at room temperature and at 4.2 K with and without applied strong magnetic fields. The cation distributions and the hyperfine parameters are determined and compared with magnetization measurements. The results show that tetragonal CuFe2O4 is an inverse spinel of Neel collinear arrangement of spins and that cubic copper ferrite is not completely inverse with a cation distribution dependent on the heat treatment.
Tetragonales und kubisches CuFe2O4-Ferrit werden hergestellt und mittels Mossbauereffekt-Methode ohne auseres Feld bzw. im starken magnetischen Feld bei Raumtemperatur und 4.2 K untersucht. Es werden Metallionenverteilung und Feinstrukturparameter bestimmt und mit den magnetischen Mesergebnissen verglichen. Die erhaltenen Ergebnisse zeigen, das tetragonales CuFe2O4-Ferrit vom inversen Spinelltyp ist mit Neelscher kollinearen Spinrichtung. Dagegen ist kubisches Cu-Ferrit teilweise von diesem Ausrichtungstyp mit einer Metallionenverteilung, die von der Warmebehandlung abhangig ist.
TL;DR: Amorphous Nb-19 at% Si alloy, prepared by rapid quenching from the molten state, was annealed while being subjected to a pressure of 10 GPA as mentioned in this paper.
Abstract: Amorphous Nb-19 at% Si alloy, prepared by rapid quenching from the molten state, was annealed while being subjected to a pressure of 10 GPA. X-ray diffraction investigations on the alloy specimens quenched to ambient conditions have shown that pressure greatly alters the crystallization characteristics and the cubic A15 (Nb3Si)-phase forms in preference to the tetragonal Nb3Si-phase at temperatures in the range from 710° C to 800° C. Up to 680° C, the component atoms do not show any tendency towards ordering upon crystallization and the body-centred tetragonal solid solution forms; while, at 830° C, niobium atoms diffuse to form the body-centred cubic Nb precipitates. Superconducting properties have been measured for the single-phase A15 structure with the lattice parametera=0.5155 nm with the results that the transition temperature,TC, is 3.4 K and the temperature coefficient of the upper critical field,HC2, is 1.2 MA m−1 K−1 (15 kOe K−1).
TL;DR: In this paper, infrared and Zeeman infrared measurements of the tetragonal symmetry cerium fluoride ion and neodymium fluoride ion charge compensation sites in calcium and strontium fluoride are reported.
Abstract: Infrared and Zeeman infrared measurements of the tetragonal symmetry cerium fluoride ion and neodymium fluoride ion charge compensation sites in calcium and strontium fluoride are reported. The neodymium results are supplemented by optical absorption and fluorescence measurements. Crystal field analyses successfully account for the observed 2F72/(4f1) and 4I92/, 4I112/(4f3) multiplet crystal field splittings and for the measured Zeeman splitting values.
TL;DR: In this article, the crystal structures of the title compounds have been determined, and the structure is the first example of a truly monomeric trihalogenomercurate (II) anion with distorted tetrahedral geometry about the mercury atoms.
Abstract: The crystal structures of the title compounds have been determined. Crystals of [NBun4](HgCl3) are triclinic, space group P(no. 2) with a= 11.011 (3), b= 11.267(3), c= 19.341(5)A, α= 87.33(2), β= 102.70(2), γ= 96.45(2)°, and Z= 4. The final R value was 0.034 for 2 187 observations. The structure is the first example established where (HgCl3)– is solely in the form of dimeric [Hg2Cl6]2– doubly chloride-bridged anions with distorted tetrahedral geometry about the mercury atoms; these anions are not centrosymmetric and although the terminal Hg–Cl bond lengths are not significantly different from one another (2.38 ± 0.01 A) the bridge is asymmetric with bond lengths 2.665± 0.01 and 2.57 ± 0.02 A. Crystals of [NBun4](HgI3) are tetragonal, space group I2d(no. 122) with a= 13.790(5), c = 26.537(5)A, and Z = 8. The final R value was 0.059 for 1 189 independent intensities measured at 200 K. The structure consists of discrete [NBun4]+ cations and [HgI3]– anions. One Hg–I bond lies on a crystallographic two-fold axis and is of length 2.683(2)A; the other two bonds are not significantly different [2.688(2)A] but make an interbond angle of 115° giving the anion C2v and not D3h symmetry. The closest approach between atoms of different anions is ca. 7.4 A precluding any significant polymeric interaction and making this the first example containing a truly monomeric trihalogenomercurate(II) anion. The [NBun4]+ groups show the expected regular tetrahedral arrangement of bonds around the N atom, but each of the n-butyl chains has the C atoms approximately co-planar, and the ion as a whole is crystallographically constrained to C2 symmetry. Vibrational spectra are rationalised in the light of the crystal structures and indicate that the anion of [NBun4](HgBr3) is dimeric [Hg2Br6]2–. The spectral detail is greatly enhanced in measurements at low temperature (ca. 100 K), especially for the dimeric anions. The structural variety shown by trihalogenomercurates is discussed.
TL;DR: In this article, a comparison of total scattering cross sections for the hydrogenated samples vs. the deuterated sample indicates a bulk hydrogen concentration of 0.21 H atoms per PbO/sub 2/ unit.
Abstract: Neutron powder diffraction data have been collected for beta-PbO/sub 2/ obtained from lead-acid battery plates cycled in H/sub 2/SO/sub 4/ and D/sub 2/SO/sub 4/. A comparison of total scattering cross sections for the hydrogenated samples vs. the deuterated sample indicates a bulk hydrogen concentration of 0.21 H atoms per PbO/sub 2/ unit. Rietveld refinements of the data yield the expected tetragonal beta-PbO/sub 2/ structure, P4/sub 2/mnm, with a 3-5% vacancy concentration on the lead sites. These results suggest that at least part of the hydrogen is incorporated into the beta-PbO/sub 2/ crystalline lattice. 21 refs.
TL;DR: In this article, the coexistence of both ferroelectric and antiferroelectric (AF) phases in one ceramic grain at room temperature is confirmed for these two compositions with TEM, and direct interfaces between F and AF domains can be observed, the former expands at the expense of the latter when bombarded by 200 keV electrons.
Abstract: 95/5 PZT ceramics with compositions of Pb(Zr1−xTix)3+1 wt% Nb2O5 (x=0.025 and 0.04) are studied with TEM. The coexistence of both ferroelectric (F) and antiferroelectric (AF) phases in one ceramic grain at room temperature is confirmed for these two compositions. The AF phase is mainly tetragonal, while a pseudo-cubic arrangement of AF polarization is also possibly present. When the Ti4+ concentration is increased, the F phase becomes predominant. Direct interfaces between F and AF domains can be observed, the former expands at the expense of the latter when bombarded by 200 keV electrons.
TL;DR: The title compound of the title compound is tetragonal, space group P4/mnc, with a = 8.136(5) A, c = 11.810(7) A and Z = 2.947(2)A.
TL;DR: In this article, the regularities relating electrophysical and structural parameters of solid solutions on the basis of lead-zirconatetitanate and sodium niobate are considered.
Abstract: The regularities relating electrophysical and structural parameters of solid solutions on the basis of lead-zirconatetitanate and sodium niobate are considered. An important structural peculiarity of these systems is a morphotropic region (MR)-region of morphotropic phase transition between tetragonal and rhombohedral (rhombic) phases. Understanding of the considered regularities makes easier the prediction of piezoceramic composition with the given properties for different applications.