High-Temperature Dielectric Response of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3: Does Burns Temperature Exist in Ferroelectric Relaxors?

It has been considered that polar nanoregions in relaxors form at Burns temperature Td approx 600 K. High-temperature dielectric investigations of Pb(Mg1/3Nb2/3)O3 (PMN) and 0.7PMN-0.3PbTiO3 reveal, however, that the dielectric dispersion around 600 K appears due to the surface-layer contributions. The intrinsic response, analyzed in terms of the universal scaling, imply much higher Td or formation of polar nanoregions in a broad temperature range, while high dielectric constants manifest that polar order exists already at the highest measured temperatures of 800 K. The obtained critical exponents indicate critical behavior associated with universality classes typically found in spin glasses

Crossover from glassy to inho‐ mogeneous-ferroelectric nonlinear dielectric response in relaxor ferroelectrics

The temperature dependence of the dielectric nonlinearities in a PMN single crystal and in 9͞65͞35 PLZT ceramics has been determined by measuring the first and third harmonic response as well as the dielectric behavior as a function of the dc electric field. In zero field a paraelectric-to-glass, and, in a high enough dc field, a glass-to-ferroelectriclike crossover in the temperature dependence of the nonlinear response have been observed. Both crossovers agree with the predictions of the spherical random-bond -random-field model. Relaxors thus undergo in zero field a transition to a spherical glass, while above the critical field a transition into a ferroelectric state occurs. PACS numbers: 78.20.Ci, 77.84.Dy The nature of the diffuse phase transition in relaxor ferroelectrics, which are typically characterized by a broad frequency dispersion in the complex dielectric constant and slowing dynamics In a system with centrosymmetrical cubic symmetry the relation between polarization P and electric field E can be written as a power series P ͑´1 2 1͒E 2´3E 3 1 . . . . This can be inverted into E a 1 P 1 a 3 P 3 1 . . . , where a 1 1͑͞´1 2 1͒ and a 3 ´3͑͞´1 2 1͒ 4 ഠ´3͞´4 1 . The temperature dependence of the dielectric nonlinearity a 3 may, in principle, provide an answer to the open question about the nature of the relaxor freezing process. The scaling theory of the second order phase transition predicts that the nonlinear dielectric coefficient a 3 should vanish at the ferroelectric transition Very recently, it has been shown that the temperature dependence of the Edwards-Anderson order parameter q EA and the dielectric nonlinearity a 3 in lead magnesium niobate (PMN) can be well described by the spherical randombond-random-field (SRBRF) model It has been pointed out In order to resolve this controversy we have conducted high resolution measurements of the temperature dependence of the dielectric nonlinearities a 3 andâ 3 measured at various frequencies and dc electric bias fields in a broad temperature range. In this Letter, we report experimental data on the dielectric nonlinearities obtained in lanthanum-modified lead zirconate titanate ceramics Pb 12x La x ͑Zr y Ti 12y ͒ 12x͞4 O 3 with x 0.09 and y 0.65 (denoted as 9͞65͞35 PLZT) and in a PMN single crystal. We show that in agreement with some previous results The 0.52-mm-thick platelet of 9͞65͞35 PLZT hot pressed ceramics was covered with evaporated gold electrodes having surface dimensions of 4.7 3 3.5 mm 2 . In the case of the PMN single crystal, where electrodes and dimensions were prepared similarly as in the PLZT 5892 0031-9007͞00͞84(25)͞5892(4)$15.0

Enhanced RCP and large inverse magnetocaloric effect of CoFe2_2O4_4 nanoparticles synthesized by auto-combustion method

This work focuses on the microstructure, magnetic properties and magnetocaloric effect of CoFe$_2$O$_4$ (CFO) nanoparticles elaborated by sol-gel auto combustion method. The XRD investigation indicates that CFO is crystallized in a cubic spinel structure and the SEM micrograph shows a fine quasi-spherical with an average grain sizes of 160 nm. The temperature dependence of the Raman spectra reveals the ferromagnetic to paramagnetic (FM-PM) transition started from 723 K and the magnetization versus temperature measurements shows the Curie temperature located at T$_{\rm C}$ = 785 K. Large value of magnetocaloric temperature change of $\Delta$T =11.2 K with a high RCP of 687.56 J Kg$^{-1}$ are achieved indirectly via the Maxwell approach making our CFO nanopowder suitable candidate for both environmentally friendly magnetic refrigeration and medical applications at ambient temperature

Room-temperature magnetoelectric effect in lead-free multiferroic (1−x)(1-x) Ba0.95_{0.95}Ca0.05_{0.05}Ti0.89_{0.89}Sn0.11_{0.11}O3_3-(x)(x)CoFe2_2O4_4 particulate composites

Multiferroic particulate composites $(1-x)$ Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$-$(x)$CoFe$_2$O$_4$ with ($x$ = 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by mechanical mixing of the calcined and milled individual ferroic phases. X-ray diffraction and Raman spectroscopy analysis confirmed the formation of both perovskite Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$ (BCTSn) and spinel CoFe$_2$O$_4$ (CFO) phases without the presence of additional phases. The morphological properties of the composites were provided by using Field Emission Scanning Electron Microscopy. The BCTSn-CFO composites exhibit multiferroic behavior at room temperature, as evidenced by ferroelectric and ferromagnetic hysteresis loops. The magnetoelectric (ME) coupling was measured under a magnetic field up to 10 kOe and the maximum ME response found to be 0.1 mV /cm/ Oe for the composition 0.7 BCTSn-0.3 CFO exhibiting a high degree of pseudo-cubicity and large density

Strontium-doping effects in solution derived lead-free ferroelectric K(0.5)Na(0.5)NbO3 thin films

Potassium sodium niobate, K0.5Na0.5NbO3 (KNN) is an environment-friendly lead-free alternative to highly efficient lead-based piezoelectrics. The poor functional properties of the KNN thin films prepared by chemical solution deposition are frequently related to the volatilisation of alkali species during processing, which hinders control over the stoichiometry, contributes to formation of secondary phases and deterioration of the microstructure. The problem can be overcome by adding alkalis in excess and/or by partial substitution of the A- and B- site atoms, such as in the case of the solid state synthesized KNN ceramics. Therefore, in this contribution, the influence of the alkaline-earth A- site dopant, Sr2+ on the microstructure, structure, and functional properties were examined for the solution-derived KNN thin films with alkaline excess. Liquid precursors of (K0.5Na0.5)1-ySryNbO3 (KNN-ySr) thin-films, where the Sr- dopant content was set at y = 0, 0.005, 0.01, were prepared from potassium and sodium acetates and niobium ethoxide in 2-methoxyethanol solvent with 5 mol% of potassium acetate excess. Strontium was introduced as acetate or nitrate. The approximately 250 nm thick KNN-ySr thin films on Pt/TiOx/SiO2/Si substrates were obtained by rapid thermal annealing at 650 oC for 5 min. According to X-ray diffraction analysis, all synthesized KNN thin films crystallize in pure perovskite phase with random orientation. The surface and cross-section microstructure analysis, performed by the field emission scanning electron microscopy, reveals that the KNN-ySr films consist of equiaxed grains, the average size of which gradually decreases from about 90 nm to a few tens of nm by increasing the Sr-dopant content. In the contribution we discuss the influence of the chemical modification on the functional response, i.e., dielectric properties versus frequency and temperature, polarisation – electric field dependence, leakage current and piezoelectric response of the as-prepared films

Influence of Synthesis-Related Microstructural Features on the Electrocaloric Effect for 0.9Pb(Mg1/3Nb2/3)O3−0.1PbTiO3 Ceramics

Despite having a very similar electrocaloric (EC) coefficient, i.e., the EC temperature change divided by the applied electric field, the 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN-10PT) ceramic prepared by mechanochemical synthesis exhibits a much higher EC temperature change than the columbite-derived version, i.e., 2.37 °C at 107 °C and 115 kV/cm. The difference is due to the almost two-times-higher breakdown field of the former material, 115 kV/cm, as opposed to 57 kV/cm in the latter. While both ceramic materials have similarly high relative densities and grain sizes (>96%, ≈5 µm) and an almost correct perovskite stoichiometry, the mechanochemical synthesis contributes to a lower level of compositional deviation. The peak permittivity and saturated polarization are slightly higher and the domain structure is finer in the mechanochemically derived ceramic. The secondary phases that result from each synthesis are identified and related to different interactions of the individual materials with the electric field: an intergranular lead-silicate-based phase in the columbite-derived PMN-10PT and MgO inclusions in the mechanochemically derived cerami

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

Electrocaloric effect and high energy storage efficiency in lead-free Ba0.95_{0.95}Ca0.05_{0.05}Ti0.89_{0.89}Sn0.11_{0.11}O3_3 ceramic elaborated by sol-gel method

Structural, dielectric, ferroelectric, energy storage properties, and electrocaloric effect were studied in lead-free ceramic Ba$_{0.95}$Ca$_{0.05}$Ti$_{0.89}$Sn$_{0.11}$O$_3$ (BCTSn) elaborated by sol-gel method. Phase purity structure was confirmed from X-ray data using Rietveld refinement analysis which revealed the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) symmetries at room temperature. Phase transitions were detected by dielectric and differential scanning calorimetry results. Energy storage properties were determined from P-E hysteresis, and the electrocaloric properties were calculated indirectly via the Maxwell approach. The large value of electrocaloric temperature change of $\Delta$T=0.807 K obtained at a relatively small field of 30 kV cm$^{-1}$ and high energy storage efficiency can make BCTSn ceramic a promising candidate for environmentally friendly refrigeration and energy storage applications