Condensation of the atomic relaxation vibrations in lead-magnesium-niobate at T=T∗T=T^*

We present neutron diffraction, dielectric permittivity and photoconductivity measurements, evidencing that lead-magnesium niobate experiences a diffuse phase transformation between the spherical glass and quadrupole glass phases, in the temperature interval between 400 K and 500 K, with the quadrupole phase possessing extremely high magnitudes of dielectric permittivity. Our analysis shows that the integral diffuse scattering intensity may serve as an order parameter for this transformation. Our experimental dielectric permittivity data support this choice. These data are important for the aplications desiring giant dielectric responses, in a wide temperature intervals and not related to electron's excitations.Comment: 6 figure

Structural, dielectric and electrocaloric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3 ceramics elaborated by sol-gel method

Ferroelectric ceramics (Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3 (x=0.00, 0.02, 0.04, 0.06) were prepared by a sol-gel method. Structural investigation revealed the co-existence of tetragonal (P4mm) and orthorhombic (Pmm2) symmetries at room temperature for the undoped ceramic, while only a tetragonal structure (P4mm) was observed for the doped ceramics. Dielectric measurements indicate a dielectric relaxation process at high temperatures which is essentially related to the hopping of oxygen vacancies. Furthermore, a down shifting of the Curie temperature (TC) with increasing Sn4+ doping rate has been revealed. The temperature profiles of the Raman spectra unveiled the existence of polar nanoregions (PNRs) above the Curie temperature in all ceramics. The ferroelectric properties were found to be related to the microstructure. Electrocaloric effect was investigated in this system that revealed an electrocaloric responsivity of 0.225 10-6 K m/V for the composition with x = 0.04 Sn doping, where other remarkable physical properties were also observed

Complex antipolar root 2 x 4 x 2 root 2 structure with Pnma symmetry in BiFeO3 and BiFe1/2Sc1/2O3: First-principles calculations

First principles calculations are done for a root 2 x 4 x 2 root 2 Pnma structure, which has been recently discussed in several attempts to describe experiments in complex magnetoelectric perovskites and which experimentally was shown to compete with several ferroelectric phases. This makes these materials extremely attracting as switchers, starters, field-stimulated capacitors, high-voltage converters, transmitters, etc. The relative energies of the root 2 x 4 x 2 root 2 Pnma structure have been calculated from first principles and analyzed as a function of pressure in BiFeO3. The stability of two polymorphs of the root 2 x 4 x 2 root 2 Pnma structure has been studied for solid solution BiFe1/2Sc1/2O3. The main distortions and relative energies of these two polymorphs in BiFe1/2Sc1/2O3, in terms of Pm (3) over barm parent symmetry, have been calculated from first principles as well

Synthesis and Crystal Structure of the Ordered Perovskite Pb FeSbO

This paper describes the synthesis of perovskite-like compound Pb2 FeSbO6 which undergoes a phase transition between 210–220 K. According to X-ray studies of the powder sample the structure of the initial cubic and the low-temperature tetragonal phases of Pb2 FeSbO6 were determined. The results obtained have been discussed using the group-theoretical analysis.В статье описывается синтез перовскитоподобного кристалла Pb2 FeSbO6 , претерпевающего фазовый переход в области 210–220 K. По данным рентгеновского эксперимента, от порошкового образца определены структуры исходной кубической и низкотемпературной тетрагональной фаз кристалла. Обсуждение результатов проводится с привлечением симметрийного анализа

Synthesis and Crystal Structure of the Ordered Perovskite Pb FeSbO

This paper describes the synthesis of perovskite-like compound Pb2 FeSbO6 which undergoes a phase transition between 210–220 K. According to X-ray studies of the powder sample the structure of the initial cubic and the low-temperature tetragonal phases of Pb2 FeSbO6 were determined. The results obtained have been discussed using the group-theoretical analysis.В статье описывается синтез перовскитоподобного кристалла Pb2 FeSbO6 , претерпевающего фазовый переход в области 210–220 K. По данным рентгеновского эксперимента, от порошкового образца определены структуры исходной кубической и низкотемпературной тетрагональной фаз кристалла. Обсуждение результатов проводится с привлечением симметрийного анализа