Search

Ceramic samples of a new perovskite multiferroic PbFe0.5Sb0.5O3(PFS) with a differing degree S of long-range compositional ordering of the Fe3+and Sb5+cations were fabricated by a variation of the high-pressure-synthesis conditions. The S values estimated from the XRD data varied from 0.93 down to 0.17. The unit cell parameter was found to decrease with increasing S. In line with these results the fraction of the singlet component in the Mössbauer spectra was found to decrease with decreasing S. However, the temperatures and diffusion of dielectric permittivity maxima as well as the temperature of magnetic phase transition determined from Mössbauer data do not change substantially with S. These results imply that PFS remains highly ordered at the nanoscale. [ABSTRACT FROM PUBLISHER]

Magnetic properties of polycrystalline multiferroic Bi0.65La0.35Fe0.5Sc0.5O3 synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions were studied using a SQUID magnetometer technique. The temperature dependent static magnetic moment M was measured in both zero-field-cooled and field-cooled modes over the temperature range of 5-300 K in low magnetic field H = 0.02 kOe. The field dependent magnetization M(H) was measured in magnetic fields up to 50 kOe at different temperatures up to 230 K after zero-field cooling procedure. A long-range magnetic ordering of the antiferromagnetic type with a weak ferromagnetic contribution takes place below TN ≈ 220 K. Magnetic hysteresis loops taken below TN show a huge coercive field up to Hc ≈ 10 kOe, while the magnetic moment does not saturate up to 50 kOe. A strong effect of magnetic field on the magnetic properties of the compound has been found. Below TN ≈ 220 K the derivatives of the initial magnetization curves demonstrate the existence of a temperature-dependent anomaly in fields of H = 15/25 kOe. The nature of the anomaly is unknown and requires additional study. [ABSTRACT FROM AUTHOR]

Results of X-ray diffraction, dielectric, and Raman studies of the ferroelectric Li0.125Na0.875NbO3solid solution obtained under hot-pressing conditions (6 GPa, 1400 and 1800 K) are compared with those of the same compound synthesized by conventional ceramics technology. The thermo-barometric synthesis is found to improve the ordering of cations and to increase the value of dielectric permittivity and ion conductivity of the ceramics. [ABSTRACT FROM PUBLISHER]

A technique for analysis of the electric modulus spectrum of dielectric ceramics based on the elimination of the direct current conductivity (σ dc) contribution has been developed. Expressions are given for the real ( M′ ac) and imaginary ( M′′ ac) parts of the complex electrical modulus related only to the dielectric polarization and not containing the contribution of σ dc. The frequency dependence of M′′ ac and the M′′ ac – M′ ac diagram for BiMg1/2Ti1/2O3 and BiMg1/2Zr1/2O3 perovskite ceramics are analyzed. [ABSTRACT FROM AUTHOR]

The dielectric permittivity of Li xNa1 − xNbO3 ferroelectric solid solutions prepared at high pressures has been measured as a function of temperature and frequency, and their structural properties have been studied. The results demonstrate that ceramics samples of the Li xNa1 − xNbO3 ( x = 0.17, 0.25) ferroelectric perovskite solid solutions exhibit superionic conduction at relatively low temperatures ( T ≥ 400 K). In the temperature range of superionic conduction, we observe significant dielectric dispersion and anomalies in permittivity, corresponding to structural transformations of the high-pressure solid solutions. [ABSTRACT FROM AUTHOR]

LixNa1 – xNbO3 (x = 0.125, 0.17, 0.25) solid solutions are synthesized at high pressures (6 GPa) and temperatures (1100–1500°C), and their polymorphic transformations are studied by x-ray diffraction. The composition and temperature dependences of lattice parameters for the identified polymorphs are presented. The results demonstrate that the high-pressure solid solutions with x = 0.17 and 0.25 are supersaturated under ordinary conditions. Heating these solid solutions to above ≃800°C leads to precipitation of an LiNbO3-based phase. [ABSTRACT FROM AUTHOR]

The ferroelectric-antiferroelectric phase transition in the Li0.12Na0.88Ta0.4Nb0.6O3 ceramic solid solution has been studied by the Raman scattering technique. As the temperature approached the transition point from below, we observed an appreciable broadening of the lines associated with the vibrations of the cations occupying octahedral and cubooctahedral cavities of the structure and with the oxygen network vibrations (which implies a substantial increase in disorder on the cation sublattices), as well as a decrease to zero intensity of the 875-cm-1 line corresponding to stretch vibrations of the bridging oxygen in the BO6 octahedral anion in the vicinity of the transition. The temperature dependence of the 875-cm-1 line intensity near the transition was used to study the behavior of the phase transition order parameter η. The behavior of η was found to disagree markedly with the Landau theory of second-order phase transitions. It is shown that discrepancies originate from the increase in disorder in the niobium and tantalum sublattices in the Li0.12Na0.88TayNb1-yO3 solid solution system with increasingly . The order of the transition is lowered. [ABSTRACT FROM AUTHOR]

Single phase ceramics with the composition Pb(Mg 0.5 Nb 0.5 )O 2.75 (PMN-V) were prepared under high pressure and temperature conditions. Cubic perovskite phase of PMN-V with a lattice parameter a = 4.0495 ± 0.0003 Å was revealed to be stable at normal pressure up to 1120 K. Temperature dependence of dielectric response of the high-pressure sintered PMN-V ceramics showed two particular regions: a diffuse ferroelectric transition with the frequency independent maximum and a typical relaxor crossover at lower temperature. Effect of high-pressure and stoichiometry (oxygen vacancies) on the B-site cation ordering and dielectric behaviour of PMN is discussed. [ABSTRACT FROM AUTHOR]

The (Ba1 – aPba)4(Pr1 – y – zBiySmz)9 + 1/3Ti18O54 compound in the ternary BaO–Pr2O3–TiO2 system and the Ba2Pr4Ti6Ta4O30, Ba3Pr3Ti5Ta5O30, Ba4Pr2Ti4Ta6O30, and Ba5Pr1Ti3Ta7O30 compounds in the quaternary BaO–Pr2O3–TiO2–Ta2O5 system are obtained by solid-phase synthesis under high (up to 7 GPa) pressure. The influence of the synthesis conditions and the partial substitution of Pb ions for Ba and Bi (or Bi/Sm) ions for Pr on the composition of the phases synthesized and their structure and dielectric properties is studied. The dielectric properties of the compounds synthesized are studied at the frequencies 102, 103, 104, and 106 Hz in the temperature range from 20 to 100°C. The synthesis modes and the Pb, Bi, Sm, and Bi/Sm concentrations necessary for the synthesis of materials with improved dielectric properties and an almost zero temperature coefficient of the resonance frequency are determined. In the ternary system of solid solutions of, the compounds with permittivity [variant_greek_epsilon] ≅ 100–110 and dielectric-loss angle tan δ ≃ 0.0015–0.003 are synthesized. In the quaternary system, the compounds with [variant_greek_epsilon] ≃ 100–150 and tan δ ≃ 0.0015–0.003 are obtained. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

A 20% substitution of Bi with La in the perovskite Bi1-xLaxFe0.5Sc0.5O3 system obtained under high-pressure and high-temperature conditions has been found to induce an incommensurately modulated structural phase. The room-temperature x-ray and neutron powder diffraction patterns of this phase were successfully refined using the Imma(0,0,γ)s00 superspace group (γ = 0.534(3)) with the modulation applied to Bi/La and oxygen displacements. The modulated structure is closely related to the prototype antiferroelectric structure of PbZr03 which can be considered as the lock-in variant of the latter with γ = 0.5. Below TN ~ 220 K, the neutron diffraction data provide evidence for a long-range G-type antiferromagnetic ordering commensurate with the average Imma structure. Based on a general symmetry consideration, we show that the direction of the spins is controlled by the antisymmetric exchange imposed by the two primary structural distortions, namely oxygen octahedral tilting and incommensurate atomic displacements. The tilting is responsible for the onset of a weak ferromagnetism, observed in magnetization measurements, whereas the incommensurate displacive mode is dictated by the symmetry to couple a spin-density wave. The obtained results demonstrate that antisymmetric exchange is the dominant anisotropic interaction in Fe3+-based distorted perovskites with a nearly quenched orbital degree of freedom. [ABSTRACT FROM AUTHOR]

A metastable perovskite BiFeo.5Sco.5O3 synthesized under high-pressure (6 GPa) and high-temperature (1500 K) conditions was obtained in two different polymorphs, antipolar Pnma and polar Ima2, through an irreversible behavior under a heating/cooling thermal cycling. The Ima2 phase represents an original type of a canted ferroelectric structure where Bi3+ cations exhibit both polar and antipolar displacements along the orthogonal [110]p and [110]p pseudocubic directions, respectively, and are combined with antiphase octahedral tilting about the polar axis. Both the Pnma and the Ima2 structural modifications exhibit a long-range antiferromagnetic ordering with a weak ferromagnetic component below TN ∼ 220 K. Analysis of the coupling between the dipole, magnetic, and elastic order parameters based on a general phenomenological approach revealed that the weak ferromagnetism in both phases is mainly caused by the presence of the antiphase octahedral tilting whose axial nature directly represents the relevant part of Dzyaloshinskii vector. The magnetoelectric contribution to the spontaneous magnetization allowed in the polar Ima2 phase is described by a fifth-degree free-energy invariant and is expected to be small. [ABSTRACT FROM AUTHOR]