Search results for "tetragonal crystal"
showing 6 items of 216 documents
Underdamped soft phonon in orthorhombic BaTiO3
1990
Abstract Raman scattering measurements are reported in orthorhombic phase and through the orthorhombic-rhombohedral transition of BaTiO3. Spectra reveal the presence of an underdamped low frequency phonon which slightly softens with decreasing temperature and abruptly stiffens at the transition to the rhombohedral phase. Results are discussed in comparison with isomorphous KNbO3 and tetragonal BaTiO3 and are interpreted as due to a dominant displacive mechanism.
Polar relaxation mode in pure and iron-doped barium titanate
1989
A dielectric relaxation peak is reported in ${\mathrm{BaTiO}}_{3}$ and in ${\mathrm{BaTi}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{O}}_{3}$. It is nearly monodispersive, centered in the ${10}^{8}$-Hz range, and slowest at the transition temperature ${T}_{c}$\ensuremath{\simeq}413 K from the cubic to the tetragonal phase. Iron doping lowers ${T}_{c}$ and slows down this relaxation mode.
Crystal structure and electronic properties of bis(mepirizole) copper(II) perchlorate. Correlation between the electronic spectrum and CuN4 chromopho…
1985
The crystal structure of the title compound has been determined from single-crystal x-ray diffraction data. The crystals are tetragonal, space group P42212, withz=2 in a unit cell of dimensionsa=b=9.575(2),c=16.135(5) A. The structure was solved by the usual Patterson and Fourier techniques, and was refined by least-squares analysis to an R value of 0.057 for 545 observed reflexions. Two mepirizole molecules are arranged in a flattened tetrahedral manner (average Cu-N, 1.974 A) around Cu, and coordinated through N atoms. The dihedral angle between N-Cu-N planes of the two ligands is 53.6+°. This geometry seems to result from steric interaction between the ligands. The e.s.r. spectrum is axi…
A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons
2001
It is shown, by means of Hartree-Fock-type calculations using the intermediate neglect of the differential overlap (INDO) method, that polaronic-type charge transfer vibronic excitons (CTVE) in ferroelectric oxides could lead to the formation of a new phase. The ground-state energy of this phase of strongly correlated CTVE lies within an optical gap of pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as ferroelectric and antiferromagnetic ordering. It is shown also that clusters of the CTVE phase being stabilized by oxygen vacancies could be responsible for the unusually strong optical Second Harmonic Generation (SHG) in nominally pure incipient ferroele…
Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide
2015
Engineering of nanoscaled structures may help controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require the combination of low thermal conductivity and low electrical resistivity. The tetragonal tungsten bronzes Nb8−xW9+xO47 (TTB) allow a continuous variation of the charge carrier concentration while fulfilling at the same time the concept of a “phonon-glass electron-crystal” through a layered nanostructure defined by intrinsic crystallographic shear planes. The thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47−δ (0 < x < 2) were studied in the temperature range from 373 to 973 K. Structural defects and the…
Design Scheme of New Tetragonal Heusler Compounds for Spin-Transfer Torque Applications and its Experimental Realization
2012
Band Jahn-Teller type structural instabilities of cubic Mn(2)YZ Heusler compounds causing tetragonal distortions can be predicted by ab initio band-structure calculations. This allows for identification of new Heusler materials with tunable magnetic and structural properties that can satisfy the demands for spintronic applications, such as in spin-transfer torque-based devices.