BiGaO3-Based Perovskites: A Large Family of Polar Materials

Solid solutions of BiGa x M 1– x O 3 ( M = Cr, Mn, and Fe) were prepared using the high-pressure high-temperature method at 6 GPa and 1700 K ( M = Cr and Fe) and 1300 K ( M = Mn). The formation of a large family of polar materials with R 3 c and Cm symmetries was found. Crystal structures were studied with laboratory X-ray powder diffraction: space group Cm, a = 5.3150(1) Å, b = 5.2960(1) Å, c = 4.6965(1) Å, and β = 92.556(2)° for BiGa 0.4 Fe 0.6 O 3; space group Cm, a = 5.2798(1) Å, b = 5.2577(1) Å, c = 4.6465(1) Å, and β = 91.974(2)° for BiGa 0.7 Mn 0.3 O 3; space group R 3 c, a = 5.51623(8) Å and c = 13.61391(17) Å for BiGa 0.4 Cr 0.6 O 3 . Samples with the Cm symmetry have square-pyramidal coordination of (Ga, M ) 3+ ions, and their structure is very similar with the structure of supertetragonal PbVO 3, BiCoO 3, and Bi 2 ZnTiO 6 materials. Samples with the R 3 c symmetry are isostructural with BiFeO 3 and have comparable calculated (based on the point-charge model) spontaneous polarization (58 μC/cm 2 for BiGa 0.4 Cr 0.6 O 3 ). The calculated polarization is 116 μC/cm 2 for BiGa 0.4 Fe 0.6 O 3, and 102 μC/cm 2 for BiGa 0.7 Mn 0.3 O 3 . BiGa 0.4 Cr 0.6 O 3 has a first-order structural phase transition at 850 K, and other polar samples showed no phase transitions below decomposition temperatures. The BiGa x Mn 1– x O 3 system demonstrated strong phase competition at 0.6 ≤ x ≤ 2/3.