Repolarization of ferroelectric superlattices BaZrO3/BaTiO3

The study was supported by Russian Science Foundation, project No. № 17-72-20105

Phase diagram of TTB ferroelectric compounds Pb1−xK2xNb2O6

Substitution of Pb with K in the PbNb2O6 phases leads to a new composition of solid solution with chemical composition Pb1−xK2xNb2O6 with x ranging from 0 to 0.34 in steps of 0.05. Ferroelectric ceramics were synthesized using solid state reaction between the corresponding oxides and carbonates. Powders are pressed and heated into ceramics and their compaction is about 92%. The tetragonal tungsten bronze (TTB) structure at room temperature was confirmed by X-ray diffraction (XRD). The temperature dependence of dielectric permittivity was measured from 35 to 600°C in the 20-106 Hz frequency range. Transition temperature decreases with the lead concentration while from x=0, with Tc=600°C and to x=0.3 with Tc=388°C.  These measurements permit to present a basical phase diagram of this family compound showing the evolution of the characteristic transition temperature Tc versus temperature. The behaviour of Tc is in agreement with theoretical study of the ferroelectric phase transition in TTB using Monte Carlo (MC) simulation. The dielectric properties of these ceramics are similar to those obtained on a single crystal and illustrate the quality of preparative conditions.Substitution of Pb with K in the PbNb2O6 phases leads to a new composition of solid solution with chemical composition Pb1−xK2xNb2O6 with x ranging from 0 to 0.34 in steps of 0.05. Ferroelectric ceramics were synthesized using solid state reaction between the corresponding oxides and carbonates. Powders are pressed and heated into ceramics and their compaction is about 92%. The tetragonal tungsten bronze (TTB) structure at room temperature was confirmed by X-ray diffraction (XRD). The temperature dependence of dielectric permittivity was measured from 35 to 600°C in the 20-106 Hz frequency range. Transition temperature decreases with the lead concentration while from x=0, with Tc=600°C and to x=0.3 with Tc=388°C.  These measurements permit to present a basical phase diagram of this family compound showing the evolution of the characteristic transition temperature Tc versus temperature. The behaviour of Tc is in agreement with theoretical study of the ferroelectric phase transition in TTB using Monte Carlo (MC) simulation. The dielectric properties of these ceramics are similar to those obtained on a single crystal and illustrate the quality of preparative conditions

Electrocaloric effect in Ba(0.2)Ca(0.8)Ti(0.95)Ge(0.05)O(3) determined by a new pyroelectric method

The present letter explores the electrocaloric effect (ECE) in the lead free oxide Ba0.8Ca0.2Ti0.95Ge0.05O3 ceramics (BCTG). The electrocaloric responsivity (dT/dE) was determined by two different methods using the Maxwell relationship (dT/dE)~(dP/dT)_E. In a first well-known indirect method, P-E hysteresis loops were measured in a wide temperature range from which the pyroelectric coefficient p_E=(dP/dT)_E and thus (dT/dE) were determined by derivation of P(T,E) data. In the second novel method the pyroelectric coefficient p_E and consequently the electrocaloric responsivity was determined by direct measurements of the pyroelectric currents under different applied electric fields. Within the experimental error good agreement was obtained between two methods with an electrocaloric responsivity equal to 0.18 +/- 0.05 10-6 K.m.V-1 was obtained at about 410 KComment: 5 pages, 4 figure

Intrinsic dead layer effects in relaxed epitaxial BaTiO3 thin film grown by pulsed laser deposition

MEM acknowledges a support from the Region of Haut de France and IPR the Ministry of Education and Science of the Russian Federation (research project 3.1649.2017/PP).Epitaxial BaTiO3 (BT) thin film of about 400 nm thickness was grown on LaSr0.5Co0.5O3 (LSCO) coated (001)MgO using pulsed laser deposition. Ferroelectric properties of the BT thin film in Pt/BT/LSCO/MgO heterostructure capacitor configuration were investigated. Dynamic P-E hysteresis loops at room temperature showed ferroelectric behavior with Ps = 32 μC/cm2, Pr = 14 μC/cm2 and EC = 65 kV/cm. Static C-V measurements confirmed reversible switching with a coercive field EC = 15 kV/cm. Basing on a model taking into account an interface dead-layer we show that the capacitance-voltage “butterfly” loops imply only 25% switching of dipoles that inferred from dynamic polarization-field loops (~ 4 and ~ 16 kV/cm, respectively). Dielectric permittivity as a function of temperature revealed a first-order ferroelectric-to-paraelectric (FE-PE) phase transition in the BT film characterized by a maximum at TC ~ 130 °C. The very large (~ 126 K at 1 kHz) difference between TC and the extrapolated Curie-Weiss temperature T0 is attributed to the dead-layer effects.PostprintPeer reviewe

Dielectric Properties Of Lead Potassium Lithium Niobate (Pb1,85K1,15Li0,15Nb5O15) With Tetragonal Tungsten Bronze (TTB) Type Structure

A new tungsten bronze ceramic oxide, Pb2-xK1+xLixNb5O15 (PKLN) (x =0.15) was prepared by high temperature solid-state reaction route. Structural and electrical properties are investigated using X-ray diffraction and dielectric measurements. Room temperature XRD pattern confirms the formation of the compound with an orthorhombic crystal system. The dielectric permittivity and the loss tangent of the sample have been measured in a frequency range 1Hz–1MHz and a temperature range 35–550 °C. Studies of dielectric properties show that the compound exhibits an anomaly at 425°C (usually called transition temperature).The electrical parameters of the material were studied using complex impedance spectroscopy showing that the compound exhibits non-Debye of relaxation process. In the paraelectric phase, activation energy was determined and the value is Eτ = 0.68 eV. The present ceramic is promising candidate for high dielectric constant and low loss dielectric ceramic.A new tungsten bronze ceramic oxide, Pb2-xK1+xLixNb5O15 (PKLN) (x =0.15) was prepared by high temperature solid-state reaction route. Structural and electrical properties are investigated using X-ray diffraction and dielectric measurements. Room temperature XRD pattern confirms the formation of the compound with an orthorhombic crystal system. The dielectric permittivity and the loss tangent of the sample have been measured in a frequency range 1Hz–1MHz and a temperature range 35–550 °C. Studies of dielectric properties show that the compound exhibits an anomaly at 425°C (usually called transition temperature).The electrical parameters of the material were studied using complex impedance spectroscopy showing that the compound exhibits non-Debye of relaxation process. In the paraelectric phase, activation energy was determined and the value is Eτ = 0.68 eV. The present ceramic is promising candidate for high dielectric constant and low loss dielectric ceramic