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Solid solutions of xBiFeO[sub 3]–yPrFeO[sub 3]–zPbTiO[sub 3] (x+y+z=1) and (1-w)BiFeO[sub 3]–wPbTiO[sub 3] have been explored for finding ferroelectromagnetic bulk material, in which ferroelectricity and ferromagnetism coexist simultaneously. The coexistence has been observed only in some ternary composition samples, that is, 0.2BiFeO[sub 3]–0.2PrFeO[sub 3]–0.6PbTiO[sub 3] and 0.4BiFeO[sub 3]–0.2PrFeO[sub 3]–0.4PbTiO[sub 3]. In the ternary solid solutions, spontaneous magnetic moments disappear with the decrease of PrFeO[sub 3] content to y<0.2 independently of BiFeO[sub 3] content. When PrFeO[sub 3] content remains constant at y=0.2, the ternary solid solutions become paraelectric with the decrease of PbTiO[sub 3] content to z≤0.2. The ferroelectromagnetic solid solutions have the noncentrosymmetric and doubled perovskite unit cell with a space group I4cm (a=bapprox. 5.4 Å, capprox. 7.9 Å). Addition of Ta[sub 2]O[sub 5] dopant substantially changes the polarization–electric-field and magnetization–magnetic field curves of the 0.2BiFeO[sub 3]–0.2PrFeO[sub 3]–0.6PbTiO[sub 3]. The binary solid solutions of (1-w)BiFeO[sub 3]–wPbTiO[sub 3] do not exhibit spontaneous magnetic moments down to 10 K over the entire composition range. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric and magnetic properties of the xBiFeO3–yDyFeO3–zBaTiO3 solid solution ceramics at high temperature range of RT ∼600°C have been characterized. For the more detailed understandings of the multiferroic property, the relation between the crystal structure transition, magnetic transition, dielectric transition with increasing temperature have been analyzed. Residual magnetization M r under the low and high applied magnetic fields (H =20Oe, 8kOe) and the dielectric properties, ɛ r and tan δ, with varying measuring frequency and temperature have been characterized using the vibrating sample magnetometer and LCR meter, respectively. The neutron diffraction data has been collected at the temperature range of RT ∼800°C. The low DyFeO3 concentration samples (y =0, 0.025) show the magnetic transitions at temperature range of 410–430°C, while the high DyFeO3 samples (y ≥0.05) show the additional transition at 250–290°C. The magnetic transition at 410–430°C corresponds to the crystal structural transition to the tetragonal P4mm from the rhombohedral R-3c, at which the BiFeO3 and the DyFeO3 samples lose their antiferromagnetic ordering. [Copyright &y& Elsevier]

The BiFeO3-BaTiO3 (BF-BT) ceramics were here prepared through the solid-state reaction of Bi2O3, Fe2O3 and nano-sized BT powders. The crystal structures and piezoelectric properties were investigated in both quenched (AQ) and slowly cooled (SC) 0.7BF-0.3BT ceramics. Prior work has shown that rhombohedral and pseudo-cubic phases coexist in 0.7BF-0.3BT ceramics. In this work, the crystal structure of the pseudo-cubic phase was refined as a non-polar orthorhombic Pbnm phase in the SC sample and as a polar orthorhombic Pmc21 phase in the AQ sample. In addition to a sharp dielectric peak at about 620 °C, corresponding to the Curie temperature of the rhombohedral phase, a broad dielectric peak with strong frequency dispersion and a sharp frequency-independent dielectric peak were observed at around 500 °C in the SC and AQ samples, respectively. We determine that the dielectric anomalies around 500 °C were caused by a relaxor phase transition of the non-polar orthorhombic phase in the SC sample and a ferroelectric–paraelectric phase transition of the polar orthorhombic phase in the AQ sample. The AQ sample showed better ferroelectric and piezoelectric properties than the SC sample. The 0.7BF-0.3BT ceramic slowly cooled in a nitrogen atmosphere showed a well-saturated P-E curve and a similar temperature-dependent dielectric constant as the AQ sample. Our results indicate that large concentrations of oxygen vacancies produce a more distorted polar orthorhombic phase and better piezoelectric properties in the AQ sample than in the SC sample. [ABSTRACT FROM AUTHOR]

Nearly half of the microwave dielectric materials includes rare-earth elements based on a database presented by Sebastian MT. The presence of rare-earth elements helps to improve the microwave dielectric properties which come from the crystal structure adjusted by the ionic radius of rare-earth. The microwave dielectrics are grouped by the crystal structure: (1) pseudo-tungstenbronze type solid solutions Ba6-3xR8+2xTi18O54, (2) homologous compounds BanLa4Ti3+nO12+3n, (3) green phases Y2BaCu2O5, (4) aeschynite LaYTiO6 and scheelite BaWO4, (5) perovskite-type compounds ABO3, (6) garnet compounds A3B'2B''3O12. The materials group (1)-(2) are presented in 'Microwave Dielectric Ceramics with Rare-earth (I)'. In this paper we discuss the groups (3)-(6). [ABSTRACT FROM AUTHOR]