A-site Of Perovskite Structure Research Articles

Achieving high pulse charge–discharge energy storage properties and temperature stability of (Ba0.98-xLi0.02Lax)(Mg0.04Ti0.96)O3 lead-free ceramics via bandgap and defect engineering

A novel dual priority strategy of strengthening charge compensation in A-site of perovskite structure and widening bandgap width was designed to prepare (Ba0.98-xLi0.02Lax)(Mg0.04Ti0.96)O3 (BLLMTx) ceramics, which can solve the conflict between polarization and breakdown strength, and improve the pulse energy storage performance of the BaTiO3-based system. As a result, ultrahigh discharge energy density of 3.98 J/cm3 and giant pulse power density of 321.6 MW/cm3 with current density of 2786.4 A/cm2 are obtained at 360 kV/cm for the (Ba0.94Li0.02La0.04)(Mg0.04Ti0.96)O3 (BLLMT0.04) ceramics with considerable fast discharge rate and outstanding temperature stability as well as cycle life, correlating with multi-ferroelectric phases coexistence, increasing bandgap width, strengthening charge compensation and establishing small size of the polar nano-regions (PNRs), which exceeds the great mass of reported lead-free ceramics. The comprehensive properties indicate that the BLLMT0.04 ceramics present potential application in pulse energy storage system. The concept of composition design via increasing bandgap width and strengthening charge compensation provides a new idea for developing lead-free dielectric ceramic capacitors.

Phase transitions in Na0.5Bi0.5TiO3-(Sr0.7Bi0.2)TiO3-PbTiO3 solid solutions

ABSTRACTIncreasing of Sr0.7Bi0.2TiO3 concentration in Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions causes increasing of Bi/Na relation and vacancies in the A-site of perovskite structure. In temperature dependence of dielectric permittivity, such a change of composition is reflected by transforming of the frequency-dependent shoulder into a maximum characteristic for relaxor ferroelectrics and diminishing of the frequency-independent maximum characteristic for Na0.5Bi0.5TiO3. Here changes in behavior of dielectric permittivity and polarization are studied if PbTiO3 is added in a certain concentration range of Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions. Changes of the characteristic temperatures as a function of PbTiO3 concentration are determined. Behavior of the electrocaloric effect is compared with the results obtained for Na0.5Bi0.5TiO3-SrTiO3-PbTiO3.

Influence of CeO2 on microstructure and microwave dielectric properties of Na1/2Sm1/2TiO3 ceramics

Crystal structures and microwave dielectric properties of wt% CeO2-added Na1/2Sm1/2TiO3 (NST) ceramics were investigated systematically (x = 0.0, 0.3, 0.6, 0.9 and 1.2). Samples with CeO2 content ≤1.2 wt% were crystallized as single phase of orthorhombic perovskite structures. When Ce4+ initially entered into the A-site of perovskite structure, uniform grain growth was observed and the dielectric constant increased, but then as Ce4+ began to enter into the B-site of the perovskite structure, abnormal grains appeared and the er value reduced. The Q × f value was firstly enhanced to its maxim value of 9640 GHz due to the improvement of density and elimination of pores as Ce4+ content was in the range of 0.0–0.6 wt%, then sharply decreased. The temperature coefficient of resonant frequency (τf) slightly decreased from 199.7 to 185.1 ppm/°C. Typically, specimens sintered in air at 1425 °C for 2 h exhibited excellent microwave dielectric properties of er = 103.01, Q × f = 9640 GHz and τf = 192.8 ppm/°C. The relationships between microwave properties and crystal structures were also discussed in this paper.

μSR study of A-site ordered perovskite manganite LaBaMn2O6

We have investigated magnetic properties of the A-site ordered perovskite manganite LaBaMn2O6 by muon spin relaxation. In the ferromagnetic metal (FM) phase below TC ~ 330 K, no muon spin oscillation is observed in the time spectra, where the muon spin relaxation significantly deviates from a single exponential form. These results may suggest a large spatial distribution of spin dynamics, i.e. the inhomogeneous magnetic nature in the FM phase of LaBaMn2O6, which has been also observed in the FM phase of A-site disordered perovskite manganites. It is, therefore, suggested that there exists the spatial distribution of spin dynamics in the FM phase of the perovskite manganites irrespective of the order/disorder at the A-site of perovskite structure.

Dielectric response of PZN-based MPB composition doped with lanthanum

Dielectric and piezoelectric properties of the lanthanum-doped morphotropic phase boundary (MPB) composition in the Pb(Zn 1/3Nb 2/3)O 3–BaTiO 3–PbTiO 3 system have been studied. Compositions of the samples were intentionally modified so that the compensation for the charge difference between La 3+ and Pb 2+ ions was realized by the increased Zn/Nb ratio. The solid solubility limit of La 2O 3 is shown to be less than 5 mol% by X-ray diffraction analysis. Rhombohedral phase is increasingly stabilized against tetragonal phase with progressive incorporation of the dopant into the A-site of perovskite structure, alternatively, the location of the MPB composition range is shifted towards PT-rich end. Moreover, it was revealed that the lattice distortion of either tetragonal or rhombohedral phase can be reduced by La-doping. The dielectric permittivity maximum ε max′ and the temperature of ε max′ are remarkably decreased by increasing La 2O 3 content, whilst the degree of the frequency-dispersion is slightly weakened. Both the degree of diffuse phase transition (DPT) and the non-Curie–Weiss behavior can be significantly promoted by La-doping.