Search

BaCo.1Bi.9O3 thin films were successfully prepared by reactive RF magnetron sputtering at different substrate temperature. Crystalline structures, surface morphologies and electrical properties were analyzed by XRD, AFM and resistivity-temperature spectrum. Co ion diffused into the lattice of BaBiO3 to form a solid solution with monoclinic perovskite structure. The root-mean-square value of surface roughness was ~ 4.2 nm for the BCB film deposited at 200 ℃. All thin films exhibited good negative temperature coefficient (NTC) thermistor characteristics. The values of B25/85, a25 and ρ25 of BaCo.1Bi.9O3 thin films were in the range of 2538–2730 K, −3.07 to −2.86% K−1 and 345.6–34634.4 Ω cm, respectively. The optimal NTC characteristic (B25/85 = 2730 K) with ρ25 of 345.6 Ω cm was presented in the BaCo.1Bi.9O3 thin films grown at 200 ℃ for 4 h. Grains and grain boundaries of BaCo.1Bi.9O3 films also showed typical NTC thermistor behavior.

Microwave dielectric ceramics of xLi1/2Ln1/2TiO3-(1-x)Na1/2Bi1/2TiO3 (Ln = Sm, 0.62 ≤ x ≤ 0.68 and Ln = Nd, 0.70 ≤ x ≤ 0.76) were prepared through a conventional solid-state reaction. X-ray diffraction analysis combined with Raman spectra indicated that the matrix phase was a continuous solid solution. The 0.64 Li1/2Sm1/2TiO3-0.36Na1/2Bi1/2TiO3 ceramic showed a very high er of 140.6, a reasonable Q·f values of 1808 Ghz, and a near-zero τf of 5.9 ppm/°C. The 0.72Li1/2Nd1/2TiO3-0.28Na1/2Bi1/2TiO3 ceramic exhibited dielectric properties of er = 151.4, Q·f = 775 Ghz and τf = 10.4 ppm/°C. As the content of Na1/2Bi1/2TiO3 continuously increased, more oxygen vacancies were generated during sample processing, resulting in a higher value of resistance.

In this work, an electric field-induced giant strain response and electric displacement, as well as temperature-dependence dielectric, impedance and energy storage densities were studied in lead-free BNT-based ferroelectric system. The XRD analysis reveals that all the investigated ceramics have a pure perovskite structure. A maximum energy storage density up to 0.907 J/cm3 at 80 kV/cm is exhibited for (1−x) Na1/2Bi1/2TiO3–xBa(Mg1/3Nb2/3)O3 ceramics at an x of 0.07. Follow-up experiments confirm that an electric-field-induced phase transition, which results in giant strain up to 0.12% at 10 Hz, is also the origin of initially weak piezoelectricity. After doping a certain amount of Ba(Mg1/3Nb2/3)O3, it is obvious that the dielectric peaks shift to low temperature and present dispersion characteristic. The increase in composition (x) can suppress grain conductivity heavily in high temperatures, thus gives a way how to adjust the nominal BNT composition for the reduction of leakage conductivity.

The (Bi0.5Na0.5)TiO3-BaTiO3 system is a promising Pb-free piezoelectric material to substitute for environmentally undesirable Pb-based ferroelectrics. However, understanding the origin of its high piezoelectric response is a fundamental issue that has remained unclear for decades. Here, complex ions (Li0.5Sm0.5)2+ were introduced to dictate the stability of the electrically-induced ferroelectric state in 0.93(Bi0.5Na0.5)1−x (Li0.5Sm0.5) x TiO3-0.07BaTiO3 relaxor ceramics. The applied electric field induces a phase transition from a non-ergodic state to a ferroelectric state as well as the realignment of ferroelectric domains. The non-ergodic relaxor state with x = 0–0.02 is accompanied by relatively high piezoelectric activity and the strongest piezoelectricity is observed near the crossover from the nonergodic to the ergodic state. The stable␣ferroelectric state cannot survive after the removal of the application electric field for the high doping level due to the enhancement of the random field, which is responsible for the rapid decrease of piezoelectric properties for x > 0.02 compositions.

Perovskite-type 0.72BiFeO3-0.28BaTi1-x Nb x O3 (BF-BTNx) ceramics were fabricated via a conventional oxide-mixed method. The phase transition behaviors, composition-dependent grain size, dielectric, ferroelectric and piezoelectric properties were investigated as a function of Nb content. The temperature dependence of dielectric permittivity showed that thermally driven normal to diffuse ferroelectric transition and Nb-doping induced normal to relaxor ferroelectric transition. Simultaneously, the butterfly shape to sprout shape transition for electric-field-induced strain curves and saturation to slim P-E hysteresis loops transition were associated with the normal-to-relaxor transition. And the low hysteresis strain curves for relaxor BF-BTNx ceramics indicated that the system was a promising candidate for high precision actuation applications. In addition, XRD results revealed that Nb-doping induced a structural transition from rhombohedral phase to pseudo-cubic phase, which may be the origin of normal-to-relaxor ferroelectric phase transition.

The ceramic system of (1−x) Li3NbO4−x Ca0.8Sr0.2TiO3 prepared by solid reaction route has been found to possess excellent dielectric properties. Li3NbO4 was combined with Ca0.8Sr0.2TiO3 to obtain a two-phase ceramic system and to achieve a thermally stable material. As x value varied from 0.1 to 0.4, the temperature coefficient of resonate frequency values (τf) ranged from +119.1 ppm/°C to −30.7 ppm/°C. At x = 0.2, the 0.8 Li3NbO4–0.2 Ca0.8Sr0.2TiO3 ceramic sintered at 1075 °C for 4 h exhibited outstanding microwave dielectric properties with a relative dielectric constant (er) ∼21.7, a quality factor (Q × f) value ∼49,276 GHz (at 6.1 GHz), and a τf ∼5.2 ppm/°C, which represented a promising candidate for microwave dielectric applications. Moreover, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were included in our work to help identify and analyze the phase assemblage and the microstructure of the sintered ceramics.

A SrO–BaO–Nb2O6–B2O3 glass–ceramic was prepared by controlled-crystallization method, and the phase evolution and dielectric properties were investigated. The correlation between the dielectric breakdown performance and the activation energy was studied by the measurements of the dielectric breakdown strength and impedance spectroscopy as a function of crystallization temperature in a SrO–BaO–Nb2O6–B2O3 glass–ceramics. It was found that dielectric breakdown strength strongly depended on the interface polarization. The crystallization temperature dependence of breakdown strength was attributed to the variation in interfacial polarization based on the results of impedance analysis. The prepared glass–ceramic crystallized at 800 °C exhibited a breakdown strength of 1050 kV/cm, a dielectric constant of 117 and a high energy storage density of 5.71 J/cm3.

Dense ceramic samples in the (1−x) BiVO4−xLi0.5Sm0.5WO4 (0.05 ≤ x ≤ 0.1) system are prepared using the solid-state reaction process. A single solid–solution phase with monoclinic structure formed through the entire compositions and the unit cell volume increases linearly with x. When x = 0.07, the composition of 0.93BiVO4–0.07 Li0.5Sm0.5WO4 readily sintered at 750 °C has excellent microwave properties with a high permittivity of 73.9, and a Q × f value of 9054 GHz and a near-zero temperature coefficient of −1.61 ppm/°C. The ceramics have applications for microwave devices requiring ultra-low sintering temperatures.