Structural, Dielectric and Ferroelectric Properties of Cu2+ and Cu2+/Bi3+ doped BCZT Lead-free Ceramics: A Comparative Study

Perovskite type Ba0.98Ca0.02Zr0.02Ti0.98O3 (BCZT), Ba0.98Ca0.02Zr0.02Ti0.976Cu0.008O3 (BCZTC) and Ba0.9725Bi0.005Ca0.02Zr0.02Ti0.976Cu0.008O3 (BCZTCB) lead-free ceramics were synthesised via solid-state reaction method at a sintering temperature of ~ 1380°C. Effects of CuO and Bi2O3/CuO doping on structural, microstructural, dielectric, and ferroelectric properties were investigated systematically. X-ray diffraction technique confirmed the existence of pure perovskite phase with the tetragonal structure in pure and in the doped BCZT ceramics at room temperature. The dielectric analysis demonstrated two anomalies around 24°C and 126°C for BCZT, which were identified as orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC) phase transition temperature, respectively. The TO-T temperature shifted to below 16°C, while the TC increased to 132°C for the BCZTCB sample. The physical mechanisms of the conduction processes were investigated through impedance spectroscopy and the values of resistance, conductivity, and activation energies associated with the grain and grain boundaries were evaluated. The activation energy was determined to be higher for doped samples than for pure BCZT. Further, the dopant-dependent ferroelectric nature of the ceramic samples was evidenced by the analysis of characteristic hysteresis loop, and a value of remnant polarisation (Pr = 4.59 µC/cm2) was obtained for the BCZTCB ceramic sample. Furthermore, the d33 value, which was 54 pC/N for pure BCZT, was determined to be 140 pC/N and 64 pC/N for BCZTC and BCZTCB, respectively.

Electrocaloric properties of Sr and Sn doped BCZT lead-free ceramics

In the present work, the electrocaloric (EC) effect in lead-free Sr and Sn doped (Ba0.85Ca0.075Sr0.075)(Zr0.1Ti0.88Sn0.02)O3 ceramic prepared by solid-state method has been investigated. The phase purity and pure perovskite phase formation with Sr and Sn doping is confirmed by X-ray diffraction. The adiabatic temperature change ΔT (due to the EC effect), entropy change (ΔS) and refrigeration capacity (RC) are estimated under various electric fields. The maximum peak values of ΔT, ΔS and RC are found as 1.5 K, 1.8 J/kg.K and 2.75 J/kg, respectively under the applied electric field of 33 kV/cm at 305 K. It is also observed that the ΔT, ΔS and RC decreases with an increase in applied temperature. Moreover, the estimated values of EC properties are significantly high which indicates that fabrication of Sr and Sn doped lead-free ceramics can be advantageous for EC applications.

Microstructural and Electrical Properties of Sn-Modified BaTiO3 Lead-Free Ceramics by Two-Step Sintering Method

Ba(Ti0.92Sn0.08)O3 lead-free ceramics were prepared using a two-step sintering (TSS) technique. Varying the first sintering temperature T1 (1400 and 1500°C) and the dwell time t1 (0, 15, and 30 min), we obtained dense ceramics which were then soaked at a constant temperature of 1000°C (T2) for 6 h (t2). The structural and electrical properties were investigated. XRD results indicated that all the ceramics showed a pure perovskite phase with tetragonal symmetry. Density and grain size increased with higher T1 temperatures and increased t1 dwell times. Enhanced electrical properties were achieved by sintering at the optimized T1 sintering temperature and t1 dwelling time. At the lower T1 sintering temperature of 1400°C, the dielectric and piezoelectric properties and the Curie temperature of the ceramics were improved significantly by increasing t1 dwell time. Further, increasing the sintering temperature T1 to 1500°C, excellent properties were obtained at t1 = 15 min which then deteriorated when t1 was increased to 30 min. The electrical properties of the sample sintered under the T1/t1/T2/t2 condition of “1500/15/1000/6” showed the best values. For this sample the piezoelectric coefficient (d33), dielectric permittivity (εr), loss factor (tanδ), and Curie temperature (TC) were 490 pC/N, 4385, 0.0272, and 48°C, respectively.

Synthesis of Modified K0.5Na0.5NbO3 Powder by Molten-Salt Technique

In the present work, the molten-salt method was applied to synthesize 0.948K0.5Na0.5NbO3–0.052LiSbO3 powder for the first time. Characteristics of the powder were investigated. Based on X-ray diffraction technique, pure perovskite phase was observed at a calcination temperature of 700 oC which is lower than that required by the conventional solid-state reaction technique for ∼200 oC. Raman spectroscopy technique showed that the powder had an orthorhombic symmetry which consistent with the X-ray diffraction results. The powder exhibited very fine grain with narrow size distribution. Particle size of the obtained powders increased with increasing calcination temperature. Therefore, the molten-salt method is a simple and effective method to synthesize 0.948K0.5Na0.5NbO3 – 0.052LiSbO3 powder.

Effects of NaNbO3 Crystals on Electrical Properties of K0.5Na0.5NbO3 Ceramics

Lead-free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics were studied and synthesized by the seed-induced method. NaNbO3 crystal was used as seed and prepared by molten salt synthesis (MSS). The average particles size of NaNbO3 seed crystal was about 1-3 mm. Then, the NaNbO3 seed was mixed with KNN powder and ball milled for 24 h. The mixed powder was calcined at 700-900 °C and sintered at 1100 °C. The phase structure and morphology of the ceramics were investigated by X-ray diffraction and scanning electron microscope and the electrical properties were studied. The results indicated that all samples showed a pure perovskite phase. The highest density of the ceramic was 93% compared to the theoretical density. The results showed that NaNbO3seed crystal improved piezoelectric properties of KNN ceramics.

The Electrical Properties of BCZT Lead-Free Ceramics Induced by BaZrO3 Seeds

Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics were produced by using the seed-induced method. The nano-particle BZ (BaZrO3) seeds were mixed with BaCO3, CaCO3, ZrO2 and TiO2 powder for preparing by the mixed oxide method. The XRD results indicated that all powder and sintered ceramic samples showed a pure perovskite phase with coexistence between rhombohedral and tetragonal phase. As the BZ seed content increased, the density of ceramics tended to decrease from 5.61 g/cm3 to 5.37 g/cm3. The average grain size of the ceramics was in the range of 12.15 -13.50 mm. The dielectric loss (tand) was less than 0.03 for all samples at room temperature (at 1 kHz). Other electrical properties, including dielectric constant (εr), remnant polarization (Pr), and piezoelectric charge coefficient (d33) values decreased with increasing BZ seed doping with relates to the decreasing grain size and density of BCZT ceramics. However, the values of coercive field (Ec) decreased and piezoelectric voltage coefficient (g33) increased with BZ seed doping.

Effect of Particle Sizes of BaTiO3 (BT) Seed on Microstructure and Electrical Properties of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3

The study was conducted to find out the effect of particle sizes of BaTiO3 (BT) seed on the microstructure and electrical properties of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics. The BT seeds were prepared by the molten salt method. Results indicated that the BT seed powder showed a single pure perovskite phase when using a low temperature of ~750°C. The particle sizes of BT seeds increased from ~381 to ~600 nm with increasing heating temperatures from 750 to 900°C. After that, the different BT seeds were mixed with BaCO3, CaCo3, ZrO2 and TiO3 via the solid state reaction method. The mixed powder was calcined and sintered at 1200 °C for 2 h and 1450 °C for 4 h, respectively. The microstructure, phase formation and electrical properties were investigated. All ceramic samples showed a pure perovskite phase. The density and average grain size values of ceramics were in the range of 5.36-5.47 g/cm3 and 9.83-11.86 μm, respectively. The highest values of dielectric constant (εr), piezoelectric constant (d33) were 3393 and 452 pC/N, respectively which obtained at the sample of BT-seed size 372 nm doped.

Comparison of Milling Techniques to Figure of Merit of 0.98PZT-0.02BYF Piezoelectric Ceramic Energy Harvester

Nowadays, the concept of harvesting energy from the environment, for example, thermal, wind, sun, vibration and human activities is much of interest. PZT is one of the materials which show an ability to harness vibration energy and then change to electrical energy. Therefore, the PZT (Pb(Zr0.53Ti0.47)O3) doped with 0.02 mol% BYF (Bi(Y0.7Fe0.3)O3) piezoelectric ceramics has been studied to improve the figure of merit (d33*g33). The PZT and BYF powder systems were prepared by solid state reaction with calcination temperature of 800 and 850 °C for 2 h, respectively. XRD results showed that both powders exhibited pure perovskite phase for PZT and single phase of BYF without pyrochlore phase. Then, the two calcined powders (PZT and BYF) were mixed according to the composition of 0.02 mol% BYF doped PZT by two different milling techniques called conventional ball-milling (CBM) and high energy ball-milling (HBM) for 10 h. The result showed that average particle size obtain from HBM was 1 µm which was smaller than from CBM shown up to a few microns in bimodal mode. The PZT-BYF-HBM ceramics showed higher physical and electrical properties but lower K value. Thus promoting to higher g33 which was equal to 36.89 * 10-3(Vm/N) and FOM was 11,632*10-15(m2/N), while PZT-BYF-CBM had g33 of 26.86* 10-3(Vm/N) and FOM at 8,016*10-15(m2/N), respectively.

Phase Structure, Microstructure and Electrical Properties of BCZT Ceramics Prepared by Seed-Induced Method

The effect of particle sizes of CaZrO3 (CZ) nanocrystal on the phase structure, microstructure and electrical properties of Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) was studied. The CaCO3 and ZrO2 were used as starting materials for CaZrO3 (CZ) seeds synthesized by the molten-salt method. The results were found that the CZ powder has a pure perovskite with the particle size about 370 to 460 nm. Then the CZ nanocrystals were mixed with the metal oxides BaCO3, CaCO3, ZrO2 and TiO2 by mixed oxide method. The phase structure, microstructure and electrical properties of BCZT ceramic were investigated as a function of particle size and concentration of CZ. The results indicated that all samples showed pure perovskite phase. The highest values of density, grain size, dielectric constant (εr) and piezoelectric coefficient (d33) were 5.50 g/cm3, 10.95 μm, 2992 and 446 pC/N, respectively which obtained at the CZ seed size 459 nm.

Influence of Cr deficiency on sintering, thermal expansion and electrical properties of La0.75Sr0.25Cr1−xO3−δ as a SOFC interconnect material

The SOFC interconnect materials La[Formula: see text]Sr[Formula: see text]Cr[Formula: see text]O[Formula: see text] [Formula: see text]–[Formula: see text] were prepared using an auto-ignition process. The influences of Cr deficiency on their sintering, thermal expansion and electrical properties were investigated. All the samples were pure perovskite phase after sintering at 1400[Formula: see text]C for 4 h. The cell volume of La[Formula: see text]Sr[Formula: see text]Cr[Formula: see text]O[Formula: see text] decreased with increasing Cr deficient content. The relative density of the sintered bulk samples increased from 93.2% [Formula: see text] to a maximum value of 94.7% [Formula: see text] and then decreased to 87.7% [Formula: see text]. The thermal expansion coefficients of the sintered bulk samples were in the range of [Formula: see text]–[Formula: see text] (30–1000[Formula: see text]C), which are compatible with that of YSZ. Among the investigated samples, the sample with 0.02 Cr deficiency had a maximum conductivity of 40.4 Scm[Formula: see text] and the lowest Seebeck coefficient of 154.8 [Formula: see text]VK[Formula: see text] at 850[Formula: see text]C in pure He. The experimental results indicate that La[Formula: see text]Sr[Formula: see text]Cr[Formula: see text]O[Formula: see text] has the best properties and is much suitable for SOFC interconnect material application.