Search results for "Solid"
showing 10 items of 3575 documents
Isomorphous ion substitutions and order-disorder phenomena in highly electrocaloric lead-scandium tantalate solid solutions
1996
Abstract The authors discuss the physical background of the electrocaloric effect in PST ceramics and its solid solutions. The most important contribution to the electrocaloric effect is due to field-induced Fm3m→R3m phase transition in the case of high long range ordering degree of B-ions in the perovskite structure ABO3.
Kinetics of dielectric response in SBN-75 ceramics at infra-low frequencies under illumination
2014
A study of the photo-dielectric effect in ferroelectric SBN-75 ceramics of a broad phase transition under light of small intensity is reported. Relations determining kinetics of the infra-low frequency dielectric response under light and after illumination are obtained from experimental measurements revealing the features of the behaviour of relaxation time constants of the dielectric polarisation with temperature.
Novel octahedral tilt system a + b + c + in (1 − x)Na0.5Bi0.5TiO3–xCdTiO3 solid solutions
2017
This work has been supported by National Research Program in the framework of project “Multifunctional Materials and composites, photonics and nanotechnology (IMIS2)”.
Dielectric and Polarization Properties of Na0.5Bi0.5TiO3-BaTiO3Solid Solutions with Na and K Niobates
2015
The role of substitution in A- and B-sites of perovskite ABO3 structure in phase transitions is evaluated, comparing (1-y)(0.939Na0.5Bi0.5TiO3-0.061BaTiO3)-yKxNa1-xNbO3 solid solutions with x = 0.0, x = 0.5 and x = 1.0. The influence of deviation from a stoichiometric Na/Bi ratio is also studied. The influence of K0.5Na0.5NbO3, NaNbO3 or KNbO3 reduces mainly to suppressing of ferroelectric properties, like in other perovskite ferroelectrics where Ti is replaced by Nb, and development of the relaxor state. Besides the frequency-dependent dielectric permittivity, the relaxor state in the studied compositions is characterized also by a temperature dependence of critical electric fields, corres…
Interpretation of the Electrocaloric Effect in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3Solid Solutions
2015
Results of direct measurements of electrocaloric effect and polarization are mutually compared in solid solutions 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3. Three temperature regions are distinguished in respect of a phase transition temperature. Above the phase transition, electrocaloric effect is determined by orientation of polar nanoregions by electric field. In wide temperature regions above and below the phase transition temperature, the difference between results, obtained from direct electrocaloric effect measurements and from polarization hysteresis loops, is explained by temperature dependence of concentration of polar nanoregions, oriented by electric field. Existence of a common Δ…
Comparative studies of ferroelectric and magnetic phase transitions in Pb(Fe1/2Nb1/2)O3-PbMO3 (M-Ti, Zr) multiferroic solid solutions
2015
Some peculiar features of magnetic x,T-phase diagram of (1-x)PbFe1/2Nb1/2O3- xPbTiO3 system at x ≈ 0.1 have been ascribed previously to the change of the lattice symmetry from rhombohedral to tetragonal or to the decrease of the lattice parameter with x. We carried out structural, dielectric, magnetization, and Mossbauer studies of (1-x)PbFe1/2Nb1/2O3-xPbZrO3 system, where the symmetry remains rhombohedral, while the lattice parameter increases with x. However, the magnetic x,T-phase diagram of (1-x)PbFe1/2Nb1/2O3-xPbZrO3 appeared to be very similar to that of (1-x) PbFe1/2Nb1/2O3-xPbTiO3. Anomalies of composition dependence of magnetic phase transition temperatures at x ≈ 0.1 are supposed …
Raman Studies of Structural Phase Transitions in Perovskite Ferroelectric Sodium Niobate Solid Solutions
2008
Raman spectra are sensitive to interactions between structural units and, consequently, may reflect fine rearrangements of the units of cation sublattice occuring at compositional changes affecting the phase equlibrium and ferroelectric properties of the crystal. Obtaining Raman spectra show the information on disordering of structural units depending on composition of the cation sublattice in real Li x Na 1 − x Ta y Nb 1 − y O 3 ferroelectrics. On the basis of experimental studies shown, that not only the frequency but also intensity of some “rigid” bands may serve as the function of order parameter of phase transition in Landau's theory of the second order phase transition.
An EPR investigation of the phase transitions and cooperative ordering phenomena of pentaamminecopper(II) polyhedra in Cu(NH3)5X2 [X=BF4, CIO4; Br]
1996
The results of powder and single-crystal EPR studies on Cu(NH3)5X2 compounds [X=BF4, CIO4; Br] give evidence that phase transitions from a cubic α-phase (g i ≃2.12) with an anti-K2PtCl6 type structure to low-temperature β-phases with reduced symmetry occur, which are induced by ordering processes of the vacancies □ of elongated [Cu(NH3)5□]2+ pseudo-octahedra. The type of order is crucially controlled, by the nature of the anion. In the case of the BF 4 − and ClO 4 − salts the large anions are structure-determining leading to a slightly disturbed antiferrodistortive order of the elongated CuIIN5 square pyramids atT c≃155 K and <130 K, respectively. The resulting pseudo-tetragonal β-structure…
Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of …
2015
We report a combined experimental and theoretical study of melilite-type germanate, Sr2ZnGe2O7, under compression. In situ high-pressure X-ray diffraction and Raman scattering measurements up to 22 GPa were complemented with first-principles theoretical calculations of structural and lattice dynamics properties. Our experiments show that the tetragonal structure of Sr2ZnGe2O7 at ambient conditions transforms reversibly to a monoclinic phase above 12.2 Gpa with similar to 1% volume drop at the phase transition pressure. Density functional calculations indicate the transition pressure at, similar to 13 GPa, which agrees well with the experimental value. The structure of the high-pressure mono…
Polymorphism and the glasslike state of cyanide mixed crystals: A mesoscopic problem.
1990
The martensitic aspect of the structural phase transitions of the alkali cyanides and their solid solutions with the alkali halides is discussed. It is suggested that the polymorphism is intimately connected with the problem of mesoscopic transformation strains. At intermediate CN concentrations a competition between glasslike inhomogeneous strains, modulated strains, and ferroelastic strains is observed.