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Bi0.6Nd0.4Fe0.5M0.5O3 (M – Mn, Cr) compositions with perovskite structure were fabricated by a high-pressure synthesis. Mӧssbauer studies have shown that doping with Nd does not change substantially Neel temperature values of Bi0.6Nd0.4 Fe0.5M0.5O3 (M – Cr, Mn) compositions. However, the Fe3+ and Mn3+ ions seem to be inhomogeneously distributed in the crystal lattice and form Fe-poor and Fe-rich regions. Similar result was obtained by us earlier for Bi(Fe1-xCrx)O3 solid solution. Both compositions studied exhibit a giant dielectric response in a wide temperature range. The giant dielectric response seems to be due to the relaxation of electrons or polarons trapped by oxygen vacancies. [ABSTRACT FROM AUTHOR]

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Photo- and cathodoluminescence in the visible range from erbium-doped barium titanate xerogels obtained in the form of a powder and a target pressed from it by explosive compaction are investigated. The powder and target exhibit upconversion luminescence of erbium ions excited at wavelengths in the regions 950–1000 and 1450–1550 nm that is characterized by strong bands at 650 and 520–560 nm and a weak band at ~820 nm that correspond to the 4F9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4I9/2 → 4I15/2 transitions of Er3+. The target also demonstrates cathodoluminescence at room temperature and liquid nitrogen temperature with the strongest bands at 650, 520, and 538 nm. [ABSTRACT FROM AUTHOR]

The electrical properties and phase states of Li0.17Na0.83NbуТа1 –уO3 (y = 0.1–0.5) ferroelectric perovskite solid solutions prepared by high-pressure, high-temperature synthesis have been studied using impedance spectroscopy. The ε'(T) and σsv(T) curves of the solid solutions have been shown to have anomalies due to phase transitions of the materials. Their Curie temperature has been found to decrease with increasing Ta concentration. The static electrical conductivity of the solid solutions has been measured as a function of temperature and the enthalpies of activation of charge carriers in them have been evaluated. The Li0.17Na0.83Nb0.1Та0.9O3 solid solution has been shown to be a high-temperature superionic conductor. Possible mechanisms of the observed phenomena are discussed. [ABSTRACT FROM AUTHOR]

Perovskite ceramics of the Bi1-xLaxFe0.5Sc0.5O3composition (0.30 ≤x≤ 0.35) that cannot be sintered in bulk form as a single phase using the conventional ceramic route were successfully prepared using the high-pressure/high-temperature technique. It has been shown that the room-temperature compositional crossover from the antipolar phase whose incommensurate modulation of displacements of Bi/La and oxygen is described by theImma(00γ)s00 superspace group to the non-polarPnmaphase occurs in the narrow range betweenx= 0.33 andx= 0.34 with no phase coexistence. The features of this compositional crossover are discussed in comparison with that observed in the Bi1-xLaxFeO3system. [ABSTRACT FROM PUBLISHER]

We report the observation of cluster (local) superconductivity in the magnetoelectric Pb(Fe1/2Sb1/2)O3 ceramics prepared at a hydrostatic pressure of 6 GPa and temperatures 1200-1800 K to stabilize the perovskite phase. The superconductivity is manifested by an abrupt drop of the magnetic susceptibility at the critical temperature Tc ≈ 7 K. Both the magnitude of this drop and Tc decrease with magnetic field increase. Similarly, the low-field paramagnetic absorption measured by EPR spectrometer drops significantly below Tc as well. The observed effects and their critical magnetic field dependence are interpreted as manifestation of the superconductivity and the Meissner effect in metallic Pb nanoclusters existing in the ceramics. Their volume fraction and average size were estimated as 0.1-0.2% and 140-150 nm, respectively. The superconductivity related effects disappear after oxidizing annealing of the ceramics. [ABSTRACT FROM AUTHOR]

In the(1-x)PbFe0.5Nb0.5O3- xPbCr0.5Nb0.5O3(PFN-xPCN) ceramics fabricated by a usual solid state synthesis route the content of the pyrochlore phase increases dramatically with x, exceeding 50% for x = 0.3 composition. Synthesis under high (6 GPa) pressure enabled us to obtain perovskite PFN-xPCN ceramics, though for compositions with x ≥ 0.4 an admixture of the pyrochlore phase was still present. Both the pseudocubic lattice parameter and ferroelectric phase transition temperature decrease monotonically as x grows. The composition dependence of the antiferromagnetic phase transition temperature for PFN-xPCN is very similar to that in the PFN-PbMO3(M-Ti, Zr, Sn) solid solution systems implying the lack of magnetic exchange between Fe3+and Cr3+ions. [ABSTRACT FROM PUBLISHER]

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]

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]