xSnxO3 Ceramics Research Articles

Structural and microwave dielectric properties of high-permittivity Ca0.245Li0.325Nd0.395Ti1−xSnxO3 ceramics

Structural and microwave dielectric properties of high-permittivity Ca0.245Li0.325Nd0.395Ti1−xSnxO3 ceramics

Enhanced electrocaloric and energy-storage properties of environment-friendly ferroelectric Ba0.9Sr0.1Ti1−xSnxO3 ceramics

The electrocaloric (EC) effect and energy storage properties of eco-friendly ferroelectric Ba0.9Sr0.1Ti1−xSnxO3 (BSTS-x) ceramics prepared by the conventional solid-state reaction method were studied. Significant energy efficiency exceeding 80% was found in our samples. In particular, BSTS-5 and BSTS-10 samples exhibit 92% and 88% efficiency, respectively, over a wide temperature range around room temperature (RT). Direct EC measurement and an indirect method based on the thermodynamic approach were used to characterize the EC effect, and both yielded consistent results. The largest electrocaloric responsivity of 0.73 K mm/kV was obtained for BSTS-0 at 368 K with an adiabatic temperature change ΔTEC of 0.55 K at a low applied electric field of only 7.4 kV/cm. With increasing Sn-content, the EC response of BSTS-x ceramics decreases, while their diffuseness increases over an extensive temperature range, centered at RT. A significant coefficient of performance (COP > 26) was found for our samples. The obtained results demonstrate the possibility of designing eco-friendly materials with higher EC effect and energy efficiency for potential solid-state refrigeration and energy storage devices.

Remarkably enhanced recoverable energy density in lead-free relaxor Ba0.94Ca0.06Ti1−xSnxO3 ceramics by the synergistic effect of nano-domains and refined grains

High-performance dielectric ceramic capacitors is a promising candidate in energy storage devices. In this work, the energy storage performance of Ba0.94Ca0.06Ti1−xSnxO3 (x = 0.04, 0.08, 0.12, 0.16) ceramics was systematically studied. Through modifying Sn4+ doping content, the breakdown strength of the ceramics is enhanced by 112.3% from 133.4 kV/cm (Ba0.94Ca0.06Ti0.96Sn0.04O3) to 283.2 kV/cm (Ba0.94Ca0.06Ti0.84Sn0.16O3). Accordingly, the recoverable energy density is greatly increased by 276.2%, that is, from 0.42 J/cm3 grow to 1.58 J/cm3. The enhanced energy storage properties could be ascribed to the following aspects: (1) the doping of Sn4+ with a larger ionic radius inhibits the migration of grain boundaries and therefore refines grains, resulting in a higher activation energy and a larger Eb; (2) the long range polar order is broke and polar nano-regions are formed, giving rise to lower energy barrier and smaller Pr; (3) the weakened ferroelectricity and delayed polarization saturation lead to higher Wrec owing to the fact that Sn4+ with d10 electronic configurations substitutes Ti4+ with d0. Our work provides a novel approach for enhancing energy storage performance in dielectric ceramic capacitors.

Effects of Sn doping on the microstructure and dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)O3 ceramics

Ba(Zr0.2Ti0.8)1−x Sn x O3 ceramics are prepared via the conventional solid state reaction method. The effects of Sn doping on microstructure, dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)1−x Sn x O3 ceramics were investigated. These results indicate that Sn4+ ions enter the unit cell maintaining the perovskite structure of solid solution and substitute preferentially for Zr4+ and then Ti4+ when Sn content (x) gradually increases from 0 to 0.2. Introduction of Sn4+ on B sites makes grain more uniform and regular. The addition of Sn4+ results in the fall of the Curie temperature. The temperature dependences of dielectric properties of Ba(Zr0.2Ti0.8)1−x Sn x O3 ceramics indicate that the addition of stannum leads to the enhancement of the diffuseness of ferroelectric–paraelectric phase transition. Moreover, it can be found that the ferroelectric properties deteriorate as Sn content increases.

Giant electrocaloric effect in lead-free Ba0.94Ca0.06Ti1−xSnxO3 ceramics with tunable Curie temperature

Electrocaloric effect in lead-free Ba0.94Ca0.06Ti1−xSnxO3 ceramics is studied using an indirect method. The Ba0.94Ca0.06Ti0.875Sn0.125O3 ceramic located near a multi-phase point shows best electrocaloric performance, which provides further experimental evidence for optimizing electrocaloric properties through constructing multiphase coexistence. Giant electrocaloric efficiency (∼0.4 K mm/kV) is achieved in this ceramic at about room temperature at a low electric field of 6 kV/cm. While large electrocaloric temperature (∼0.63 K) is obtained by further enhancing electric field (20 kV/cm), a decrease in electrocaloric efficiency (0.32 K mm/kV) is simultaneously observed, which is attributed to phase transition from first-order to more diffusive second-order under higher electric field.

Structure and microwave dielectric properties of (Zn0.3Co0.7)Ti1−xSnxO3 ceramics

Low-loss ceramics (Zn0.3Co0.7)Ti1−xSnxO3 (ZCTS) (x = 0, 0.02, 0.05, 0.09, 0.14) were prepared by the conventional solid-state route. The effects of Sn ratio on phase composition, microstructure, and the microwave dielectric properties of (Zn0.3Co0.7)Ti1−xSnxO3 materials were investigated using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). The results revealed that the ZCTS (x = 0.02, 0.05, 0.09, 0.14) composites consisted of three crystalline phases: ZnTiO3-type phase, Zn2TiO4-type phase, and TiO2 phase. Due to the compensating effect of rutile TiO2, the temperature coefficient of resonant frequency (τf) for (Zn0.3Co0.7)Ti1−xSnxO3 (x = 0.02) ceramic was tuned to near zero value. It was found in our experiment that with the increase of Sn ratio, the microwave dielectrics showed a great promotion in Q × f when Ti4+ was partially substituted by Sn4+. Typically, the (Zn0.3Co0.7)Ti1−xSnxO3 (x = 0.02) ceramic sintered at 1,220 °C for 4 h exhibited good microwave dielectric properties of er = 24, Q × f = 66,700 GHz and τf = −5.43 ppm/°C.

Effect of Sn content on dielectric, piezoelectric and ferroelectric properties for Pb(Zr0.35Ti0.65)1−xSnxO3 ceramics near morphotropic phase boundary

ABO3 perovskite structure Pb(Zr0.35Ti0.65)1−xSnxO3 (PZST) piezoelectric ceramics were synthesized by conventional solid state reaction method with the compositions near tetragonal to rhombohedral morphotropic phase of boundary (MPB). The influences of Sn content on dielectric, piezoelectric and ferroelectric properties of PZST piezoceramics were investigated while Zr/Ti ratio was fixed. With increasing Sn content, the c/a ratios and Curie temperatures TC decrease monotonically. Rayleigh law was explored to evaluate the piezoelectric behaviors as a function of loading electric field strength. Both Rayleigh coefficients αd and dinit′ are increased with increasing Sn content, indicating that Sn content considerably increase the mobility of domain walls and also the piezoelectric nonlinear responses.

Enhanced electrocaloric effect in lead-free BaTi1−xSnxO3 ceramics near room temperature

The electrocaloric effect in lead-free BaTi1−xSnxO3 (BTSn, x = 0.08, 0.105, and 0.14) ferroelectric ceramics was studied by using an indirect method. It was found that the largest electrocaloric response could be achieved in BTSn with x = xQP = 0.105 near room temperature with an adiabatic temperature change ΔT of 0.61 K and an electrocaloric strength ΔT/ΔE of 0.31 K mm kV−1, under a modest electric field ΔE of 20 kV cm−1, which is comparable with the best values reported in lead-free materials. These enhanced values are attributed to the multiphase (four phases) coexistence at x = xQP corresponding to the quasi-quadruple point composition.

Non-linear permittivity study of the crossover from ferroelectric to relaxor and cluster glass in BaTi1−xSnxO3 (x = 0.175–0.30)

The electric susceptibilities χ1, χ2, and χ3 of BaTi1−xSnxO3 ceramics with 0.175 ≤ x ≤ 0.30 are measured at 90 ≤ T ≤ 350 K and 37 ≤ f ≤ 106 Hz. Crossover from ferroelectric (x = 0.175) to relaxor behavior (x = 0.30) via coexistence of both (x = 0.25) is indicated by increasing polydispersivity and suppression of χ2 intensity. The relaxor properties are due to weak random fields acting on dipolar Ti4+ clusters in non-polar Sn4+ environment. Upon cooling frustrated interaction between the blocked polar nanoregions yields a cluster glass ground state for x = 0.30 as verified by the dynamic criticality of χ1, χ3, and the scaled non-linear susceptibility a3.

Dielectric properties and structural defects in BaTi1−xSnxO3 ceramics

As a function of Sn doping concentration x, dielectric properties and X-ray diffraction measurements were carried out on BaTi1-xSnxO3 (BTSx) ceramics fabricated by the solid-state reaction route. Positron annihilation lifetime spectroscopy and coincident Doppler-broadening spectroscopy were also measured for the evaluation of defects in the BTSx ceramics. Dielectric properties measurement reveals that the permittivity of BTSx ceramic gradually increases with increasing Sn dopant content for x≤3%, and then decreases. This change of permittivity is found to agree well with the relative defect concentration estimated using two positron annihilation techniques. The S-W plot indicates that the defect species do not change with Sn doping. The variation correlations between defects and dielectric properties further proves that BTSx ceramics with the higher relative defect concentration present a lower permittivity.

Diffuse phase transition in BaTi1−xSnxO3 ceramics: An intermediate state between ferroelectric and relaxor behavior

Dielectric relaxation and polar structures of BaTi1−xSnxO3 ceramics, x=0.10–0.20, are investigated by means of dielectric spectroscopy and piezoresponse force microscopy. A transition regime between “normal” ferroelectric and relaxor behaviors is encountered. In the compositions with x=0.10, a complex domain pattern confirming the ferroelectric state is observed. Strong dielectric relaxation around Tm is attributed to domain wall motion. On the other hand, the dielectric spectra in the sample with x=0.20 are very similar to those observed in relaxor ferroelectrics. Analysis of the relaxation spectra at the intermediate concentration, x=0.15, reveals both domain wall response and an additional contribution related to mesoscale polar structures. The appearance of relaxor behavior in BaTi1−xSnxO3 is discussed within the framework of the random field model.

AC-Poling of Functionally Graded Piezoelectric Bending Devices

Monolithic ceramics with an uniaxial gradient of piezoelectric and/or dielectric coefficients (functionally graded materials—FGM) are suitable for bending actuators with strongly reduced internal mechanical stresses. We prepared BaTi1—xSnxO3 ceramics with a Sn-content of 7.5 mol% (BTS7.5) at the upper side and 15 mol% (BTS15) at the lower side. Two sheets of powder with different stoichiometry were pressed and sintered. The gradient of stoichiometry was modified by additional layers of powder with 10 and 12.5 mol% Sn, respectively. The Sn content after sintering across the thickness was investigated by Electron Probe Micro-Analysis (EPMA). The gradient of the chemical composition was transformed into a functionally gradient of the electromechanical properties by a poling process. An increasing of the bending deflection was obtained by cycling with an unipolar AC-voltage. In this work we studied two effects which can explain this behavior.