Search results for "tetragonal crystal"
showing 10 items of 216 documents
Effect of germanium addition on the properties of reactively sputtered ZrN films
2005
For the first time, Zr-Ge-N films were deposited on silicon and steel substrates by sputtering a Zr-Ge composite target in reactive Ar-N2 mixture. The films were characterised by electron probe microanalysis, X-ray diffraction, micro-Raman spectroscopy and depth-sensing indentation. The effects of the Ge content and substrate bias voltage on the films' structure, internal stress, hardness and oxidation resistance were investigated. Substrate bias strongly influenced the chemical composition of the films being observed by means of a steep decrease in the Ge content for negative bias voltages higher than -80 V. In these cases, a significant hardness improvement was registered. For -100 V bias…
Effects of CuO doping on structure, microstructure and dielectric properties of BaTiO3–PbTiO3 solid solution
2019
Ba0.7Pb0.3TiO3 and Ba0.7Pb0.3TiO3+yCuO (y = 0.1 wt%, 0.5 wt%, 1 wt% and 3 wt%) samples were prepared by a solid state reaction method. High purity raw materials were used. Structural properties of the sintered pellets were studied by X-ray diffractometer X’Pert PRO (PANalytical). A single phase of perovskite structure with tetragonal phase was identified at room temperature. The surface morphology of the obtained specimens was characterized by the scanning electron microscopy (Hitachi S4700). The investigations has shown that the synthesized ceramic materials are characterized by the high density, homogeneity of microstructure and low porosity. Dielectric spectroscopy was used to study the …
Lattice Instability and Competing Spin Structures in the Double Perovskite InsulatorSr2FeOsO6
2013
The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, 57Fe Mossbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.
Spintronic properties of Li1.5Mn0.5Z (Z=As, Sb) compounds in the Cu2Sb structure
2015
Abstract We have investigated the spintronic properties of two formula units of Li1.5Mn0.5Z (Z=As, Sb), in the Cu2Sb tetragonal crystal structure based on first-principles density-functional theory calculations, at, and near, their equilibrium (minimum total energy) lattice constants. Two groups of configurations, A and B, are formed for each type of alloy by interchanging Mn with each Li located at four different positions with respect to Li4Z2. Mn has four nearest neighbors in group-A and has one nearest neighbor in group-B. The bonding features of the alloys are compared to the ionic bonding in Li4Z2, and the tetragonal structure of cubic LiMnZ. The magnetic moments of these compounds ar…
Lattice dynamics study of scheelite tungstates under high pressure I.BaWO4
2006
Room-temperature Raman scattering has been measured in lead tungstate up to 17 GPa. We report the pressure dependence of all the Raman modes of the tetragonal scheelite phase PbWO4-I or stolzite, space group I41 /a, which is stable at ambient conditions. Upon compression the Raman spectrum undergoes significant changes around 6.2 GPa due to the onset of a partial structural phase transition to the monoclinic PbWO4-III phase space group P21 /n. Further changes in the spectrum occur at 7.9 GPa, related to a scheelite-to-fergusonite transition. This transition is observed due to the sluggishness and kinetic hindrance of the I → III transition. Consequently, we found the coexistence of the sche…
Emergence of a metallic metastable phase induced by electrical current in Ca2RuO4
2019
A comprehensive study of the behavior of the Mott insulator ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ under electrical current drive is performed by combining two experimental probes: the macroscopic electrical transport and the microscopic x-ray diffraction. The resistivity, $\ensuremath{\rho}$, versus electric current density, $J$, and temperature, $T,\ensuremath{\rho}(J,T)$, resistivity map is drawn. In particular, the metastable state, induced between the insulating and the metallic thermodynamic states by current biasing ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ single crystals, is investigated. Such an analysis, combined with the study of the resulting ${\mathrm{RuO}}_{6}$ octahedra energy le…
Comparative X-ray diffraction study of the crystalline microstructure of tetragonal and monoclinic vanadium–zirconium dioxide solid solutions produce…
2009
The microstructural characteristics of solid solutions, prepared by heating dried gel precursors with nominal compositions VxZr1−xO2(0 ≤x≤ 0.1) at 723 and 1573 K, were determined from X-ray diffraction patterns. The crystalline microstructure of the resulting specimens, characterized by a prevalent crystallite shape, a volume-weighted crystallite size distribution and a second-order lattice strain distribution, was found to depend on the vanadium content. A characteristic feature of all size distributions was their bimodality, explained as a result of transformations between tetragonal and monoclinic phases during thermal treatment. A comparative study of the microstructure of both zirconia…
Are Metal-Free Monolithic Crowns the Present of Prosthesis? Study of Mechanical Behaviour
2019
Purpose: To analyze in vitro the mechanical behavior of five types of complete coverage crowns fabricated from different materials. Materials and methods: Seventy-five full coverage crowns were divided into five groups according to material: Group I, metal core with feldspathic ceramic covering (MC- control group)
Low-temperature metastabilization of tetragonal V+4-containing ZrO2 solid solutions
2001
Abstract The formation and characterization of tetragonal vanadium–zirconia solid solutions with different vanadium contents have been investigated. Vanadium–zirconia precursors were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetonate, and studied over the range of temperature up to the tetragonal–monoclinic phase transformation. The formation of the tetragonal phase has been investigated by X-ray powder diffraction (XRD). It was found that it took place after annealing around 450°C for all specimens independently of the vanadium loading. In contrast, the temperature for the subsequent tetragonal to monoclinic transformation was dependent on the nominal vanadiu…
X-Ray Crystallographic Analysis of the Charge-Density Wave Modulated Phases in the NbTe4-TaTe4 System
1999
NbTe4 and TaTe4 belong to the important structural family CuAl2 (tl20) characterized by a tetragonal antiprismatic coordination of the minority component. The basic structures were first described by Selte and Kjekshus [1] and Selte and Bjerkelund [2]. In these structures the Te atoms form 1-D infinite columns of stacked tetragonal antiprisms along [001] which are centered by the metal atoms (Figure 1). The arrangement of the antiprismatic columns in the tetragonal a 1 a 2-plane yields short Te-Te contacts, forming Te2 pairs with covalent bonds of about 2.92 A. Thus, following the usual chemical arguments MTe4 (M=Nb,Ta) is a ditelluride of M(IV), i.e. M4+(Te 2 2- )2. The structure is strong…