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Ferroelectric BiFeO3 and paraelectric Bi0.8Ca0.2FeO3 polycrystalline films were prepared to study the dependence of resistive switch on defect density. With defect density and the corresponding leakage current increasing, current-voltage loops allow four different types, i.e., overlapping, hysteresis without memory effect, bipolar resistive switch, and unipolar resistive switch. The first three types can transform to the last one, once electroforming introduces enough charged defects to films and the resistance monotonically increases to a certain value. Unipolar resistive switch is due to conductive filamentary type and can be treated as an especial electroforming process. Furthermore, its high resistance status allows the second or third type at low voltage region. [ABSTRACT FROM AUTHOR]

0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 ceramic and its epitaxial films on (0 0 1) SrTiO3 substrate were prepared to compare their dielectric and ferroelectric properties. The ceramic has a high dielectric permittivity, a weak dielectric relaxation, a low ferroelectric Curie temperature ( TC) of 60°C and a fast polarization relaxation. The films show much lower dielectric permittivities and mild dielectric relaxations. Furthermore, the TC of film with 40, 100, and 200 nm thickness is 155°C, 110°C, and 60°C, respectively, because the epitaxial strain decreases with the film thickness increasing. The higher the TC is, the more stable the room-temperature polarization is. [ABSTRACT FROM AUTHOR]

0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 ceramic and its epitaxial films on (0 0 1) SrTiO3 substrate were prepared to compare their dielectric and ferroelectric properties. The ceramic has a high dielectric permittivity, a weak dielectric relaxation, a low ferroelectric Curie temperature ( TC) of 60°C and a fast polarization relaxation. The films show much lower dielectric permittivities and mild dielectric relaxations. Furthermore, the TC of film with 40, 100, and 200 nm thickness is 155°C, 110°C, and 60°C, respectively, because the epitaxial strain decreases with the film thickness increasing. The higher the TC is, the more stable the room-temperature polarization is. [ABSTRACT FROM AUTHOR]

Abstract: With a rhombohedra-like structure, the Bi0.875Sm0.125FeO3 ceramics show much-improved ferroelectric and piezoelectric properties: a saturated ferroelectric polarization of 40μC/cm2 and a piezoelectric d 33 of 45pC/N at 20°C. After the polarized sample was annealed at 600°C, its d 33 decreases to ∼20pC/N. Besides, Bi0.875Sm0.125FeO3 shows dielectric or impedance resonances at 20–550°C, suggesting that the ferroelectric component with high Curie temperature still partially remained at 550°C. However, the impedance and the resistance decrease so fast with temperature increasing that both of them are below 1000ohm above 420°C. Even so, this piezoelectric resonance method can explore leaky ferroelectrics at high temperature. [Copyright &y& Elsevier]

Abstract: Insulated Bi1− x Dy x FeO3 (x =0–0.2) were prepared to study their multiferroic properties at various temperatures. Bi1− x Dy x FeO3 (x =0–0.08) shows rhombohedral phase, ferroelectric polarization of >18μC/cm2, and piezoelectric d 33 value of >35pC/N at room temperature. After the polarized ceramics were annealed at various high temperatures, the piezoelectric d 33 changes suggest that ferroelectric component exists below 700°C. There are ferroelectric phase and PZT-like anti-polar orthorhombic phase together in Bi1− x Dy x FeO3 (x =0.11–0.17), although only ferroelectric phase contributes polarization and d 33 which decreases with Dy concentration at this two-phase coexistence region. Finally, Bi1− x Dy x FeO3 (x =0.2) transforms to non-polar orthorhombic phase according to structural and electric measurements. [Copyright &y& Elsevier]

Abstract: Insulated Bi1−x Sm x FeO3 () were prepared to study their multiferroic properties at various temperatures. Bi1−x Sm x FeO3 () shows a rhombohedral-like phase, ferroelectric polarization of >17.8 μC/cm2, piezoelectric value of >35 pC/N at room temperature. Bi1−x SmxFeO3 () has a ferroelectric triclinic phase and an anti-polar orthorhombic phase together at room temperature, and Bi0.75Sm0.25FeO3 is mainly composed of a non-polar orthorhombic phase. After the polarized Bi1−x Sm x FeO3 () was annealed at various high temperatures, the evolution supports ferroelectric component exist above 500 °C. Raman spectra suggests that the main component of Bi0.875Sm0.125FeO3 does not keep a rhombohedral ferroelectric phase above 400 °C, thus its ferroelectric traits at high temperature should be due to ferroelectric clusters embedded in orthorhombic phase. [Copyright &y& Elsevier]