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The Mössbauer spectra of PbFe0.5Ta0.5O3 samples prepared by mechanical activation of a mixture of PbO, Fe2O3, and Ta2O5 with subsequent annealing at different temperatures Ta have been investigated. The Mössbauer study showed that Fe3+ ions in these samples can be either in the octahedral coordination or in the state with a coordination number equal to 5, which indicates the presence of oxygen vacancies in the samples. The magnetic-phase transition temperatures TM are found for all samples. The dependence of TM on Ta is peaking in the vicinity of Ta ≈ 700°C. The factors affecting the TM values of the mechanically activated PbFe0.5Ta0.5O3 samples are discussed. [ABSTRACT FROM AUTHOR]

The concentration dependences of the magnetic phase transition temperature TN, determined based on the changes in Mössbauer spectra, were investigated for a BiFeO3 solid solution with ordered perovskite PbFe0.5Sb0.5O3 and for a disordered BiFe1 –xCrxO3 solid solution. It is established that the magnetic-order type in BiFe1 –xCrxO3 changes from antiferromagnetic to spin-glass at a higher degree of Fe-sublattice dilution in comparison with the PbFe0.5Nb0.5O3-based solid solutions presumably because of the smaller BiFeO3 lattice parameter. Due to the local ordering of Fe3+ and Sb5+ ions, the TN value decreases more rapidly (as compared to BiFe1 –xCrxO3) with a decrease in the Fe3+ content in the lattice of (1 – x)BiFeO3– xPbFe0.5Sb0.5O3 solid solutions. [ABSTRACT FROM AUTHOR]

Temperature dependences of the dielectric permittivity ε of (1−x)PbFe0.5Nb0.5O3-x BaFe0.5Nb0.5O3 solid solution ceramics at 100 Hz–1 MHz have been studied in the 12–500 K temperature range. To lower the conductivity values and exclude the corresponding relaxations, 1 wt% of Li2CO3 was added to the starting mixture of oxides. It was found that Li-doping is effective in lowering the conductivity only for compositions with x ≤ 0.5. T he permittivity–temperature dependences of the (1−x)PbFe0.5Nb0.5O3–xBaFe0.5Nb0.5O3 compositions were found to change, as x grows, from relatively sharp frequency-independent maxima typical of usual ferroelectrics to the diffused and frequency-dependent maxima typical of relaxors and then to the saturated at low temperatures and frequency-independent ε(T) curves typical of incipient ferroelectrics and at last, to the step-like frequency-dependent ε(T) curves known for the dielectrics with Maxwell–Wagner-type polarization. The ε value of BaFe0.5Nb0.5O3 at 20 K measured at 1 MHz does not exceed 30. The character of the evolution of dielectric properties in the (1−x)PbFe0.5Nb0.5O3–x BaFe0.5Nb0.5O3 system and low ε value of BaFe0.5Nb0.5O3 implies that BaFe0.5Nb0.5O3 is a paraelectric rather than ferroelectric relaxor. [ABSTRACT FROM AUTHOR]

Ceramic PbFeCrNbO ( x = 0.025, 0.05, 0.10, 0.15) perovskite solid solutions are synthesized using a solid-state reaction method. The samples of solid solutions are studied using the methods of X-ray diffraction, dielectric, Mössbauer and X-ray photoelectron spectroscopy, electron microscopy, and X-ray microanalysis. XRD studies have shown that the content of the parasitic pyrochlore phase increases dramatically with x, approaching 50% for x = 0.15. The averaged lattice parameter and the temperature of ferroelectric phase transition decrease monotonically with x. Concentration dependence of the magnetic phase transition temperature for PbFeCrNbO is very similar to that in the Pb(FeNb)MO (M = Ti, Zr, Sn) solid solutions implying the lack of magnetic exchange between Fe and Cr ions. Bulk and surface elemental compositions are found to differ from each other and from nominal composition. XPS studies revealed that the PbFeCrNbO ( x = 0.05, 0.10) samples contain Cr, Cr, Cr, and Cr ions. It is assumed that the presence of Cr and Cr ions is due to the formation of a small amount of non-perovskite phases, e.g., PbCrO and FeCrO. This assumption is supported by the presence of weak reflections of the Pb CrO phase in the XRD pattern of the composition with x = 0.15. [ABSTRACT FROM AUTHOR]

Temperature dependences of specific heat C ( T) and coefficient of thermal expansion ;(T) for NaLiNbO sodium-lithium niobate ceramic samples are investigated in the temperature range of 100-800 K. The C ( T) and α( T) anomalies at T = 310 ± 3 K, T = 630 ± 8 K, and T = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ↔ Q ↔ S( R) ↔ T2( S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition Q → R/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the C ( T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed. [ABSTRACT FROM AUTHOR]

We have observed the magnetoelectric (ME) response at room temperature and above in high-resistive ceramics made of multiferroic Pb(FeNb)O (PFN) and PFN-based solid solution 0.91PFN-0.09PbTiO (PFN-PT). The value of the paramagnetoelectric (PME) coefficient shows a pronounced maximum near the ferroelectric-to-paraelectric phase transition temperature, T and then decreases sharply to zero for T > T. The maximal PME coefficient in PFN is about 4 × 10 s/A. The theoretical description of the PME effect, within the framework of a Landau theory of phase transitions allowing for realistic temperature dependences of spontaneous polarization, dielectric and magnetic susceptibilities, qualitatively reproduces well the temperature dependence of the PME coefficient. In particular, the Landau theory predicts the significant increase of the PME effect at low temperatures and near the temperature of the paraelectric-to-ferroelectric phase transition, since the PME coefficient is equal to the product of the spontaneous polarization, dielectric permittivity, square of magnetic susceptibility, and the coefficient quantifying the strength of the biquadratic ME coupling. An atomistic technique is further developed and used to further demonstrate that the PME effect can also be sensitive to the frequency of the applied magnetic field (when this frequency is of the order of GHz). [ABSTRACT FROM AUTHOR]

The spectral dependences of photostimulated currents in single crystals of lead magnoniobate and lead magnoniobate titanate are investigated. The results suggest that the distribution of the density of impurity states in the bandgap of the studied crystals is quite wide. These levels could participate in the formation of diffuse phase transitions. [ABSTRACT FROM AUTHOR]

Dielectric, X-ray, Mossbauer and magnetization studies of (1 − x)PbFeTaO-( x)PbTiO ceramics with 0 ≤ x ≤ 0.3 have been carried out to determine the compositional evolution of ferroelectric and magnetic phase transition temperatures. Addition of PbTiO to PbFeTaO increases the temperature T of the dielectric permittivity maximum, decreases both the diffusion of this maximum and its frequency dependence. However, the Curie-Weiss temperature exceeds T for all the compositions studied, indicating that the phase transition still remains diffused. Dilution of the (Fe, Ta)-sublattice by Ti lowers the Neel temperature T but above a certain compositional threshold ( x ≈ 0.1) fast lowering of T stops and a new magnetic state stable in a rather wide compositional range appears. Large difference between the zero-field-cooled (ZFC) and FC magnetization-temperature curves as well as between the temperatures of magnetic phase transition determined from Mossbauer and magnetization studies for compositions with x > 0.1 implies that this state is a spin-glass phase. [ABSTRACT FROM AUTHOR]

An amorphous material based on lead iron niobate (PFN) is studied by X-ray diffraction and dielectric and Mössbauer measurements over a wide temperature range. The atomic structure of amorphous PFN is found to be substantially disordered, which suppresses the transitions into ordered states in the electric and magnetic dipole subsystems that are inherent in crystalline PFN. The dependence of electrical conductivity σ on field frequency ω is shown to correspond to the law σ ∼ ω s , where parameter s decreases linearly with increasing temperature. This law corresponds to a hopping carrier transfer mechanism that is correlated due to the Coulomb interaction. [ABSTRACT FROM AUTHOR]

The effect of a bias field E on the value and temperature dependence of permittivity ɛ of ceramic samples of solid solutions 0.6NaNbO-0.4 NaTaO (I), and 0.97[0.9NaNbO-0.1NaBiTiO]-0.03LiNbO (II) possessing an anomalously large temperature hysteresis of ɛ( T) dependence is studied. The character of the dependences of both the height and the temperature of the ɛ( T) maximum on the field show that composition (I) has antiferroelectric properties, while composition (II) has ferroelectric properties. It is found that up to 8 kV/cm, the strength of the bias field has actually no effect on the width of the ɛ( T) temperature hysteresis of the compositions under study. [ABSTRACT FROM AUTHOR]

The effect of a bias electric field on the value and temperature dependence of dielectric permittivity ɛ of lead-free ceramics of the NaNbO-SrNbO-LiNbO system with diffuse maximum ɛ( T) (temperature T of which is strongly dependent on frequency) was studied. It was found that the ɛ( T) maximum decreases and diffuses as the electric field strength E increases, while T is virtually independent of E in the investigated range of E ≤ 8 kV cm. A similar effect of a bias electric field on ɛ and T was observed earlier in classical lead-containing relaxors of the PbMgNbO type. [ABSTRACT FROM AUTHOR]

(1 − x)PbFeNbOPbTiO ( PFN- xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x- T phase diagram of the PFN-xPT system was determined for the first time. [ABSTRACT FROM AUTHOR]

It is established that, as a result of application of even a small (∼0.5 kV cm−1) bias field E, the maximum of the piezoelectric coefficient d 31 in (1 − x)Pb(Mg1/3Nb2/3)O3 − xPbTiO3( x = 0.06, 0.13) crystals shifts from the Vogel-Fulcher temperature to the critical point in the E- T phase diagram of a given composition. The field dependence of the d 31( T) peak magnitude has a maximum near the E values corresponding to the critical point. [ABSTRACT FROM AUTHOR]