BiGaO₃-Based Perovskites: A Large Family of Polar Materials

Abstract

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 R3c 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 R3c, 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 R3c 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.

Electronic structure, ferroelectric properties, and phase stability of BiGaO3 under high pressure from first principles

“…For these solid solutions large values of spontaneous polarization were predicted using the point charge model, i.e., 58 lC/cm 2 for BiGa 0. 4 [7]. The supertetragonal-like structure was observed in BiFe 0.6 Ga 0.4 O 3 thin films [8].…”

“…Experimentally established structural data from Refs. [7,10] were used as input for the calculations. The Brillouin zone integrations were performed using 12 9 12 9 12, 8 9 8 9 8, 8 9 8 9 8, and 6 9 6 9 6 Gamma-centered k-point grids for cell with 5-(Pm3m, P4mm, R3m), 10-(C2/m, Cm, R3c, R-3c), 20-(C2/c, Cmcm, Imma, Pcca, Pnma), and 40-atoms (Pbam), respectively.…”

“…The giant ferroelectric polarization of 230 lC/cm 2 for BiGa 1-x Fe x O 3 [6] and 150 lC/cm 2 for BiFe 0.6 Ga 0.4 O 3 [8] was found. The nonpolar orthorhombic (space groups Imma and Pnma) and monoclinic (space group C2/c) phases were observed in bulk BiCr 1-x Ga x O 3 [7,9] and BiMn 1-x Ga x O 3 [7]. In the first report on structural behavior of BiGaO 3 as a function of pressure, Yusa et al [10] showed that it undergoes three pressure-induced phase transitions in the 0-11 GPa range, from pyroxene structure (Pcca space group) to the perovskite-like monoclinic Cm phase, and then to the orthorhombic Cmcm, and finally from Cmcm to Pbam structure at 3.2, 6.3, and 9.8 GPa, respectively.…”

“…Further experimental investigation revealed that perovskitelike structures appear under chemical or hydrostatic pressure. The coexistence of polar rhombohedral (space group R3c) and monoclinic (space group Cm) phases was observed in solid solution BiFe 1-x Ga x O 3 at x = 0.1 [6] and x = 0.2-0.4 [7] and BiCr 1-x Ga x O 3 at x = 0.8 [7]. For these solid solutions large values of spontaneous polarization were predicted using the point charge model, i.e., 58 lC/cm 2 for BiGa 0.…”

“…But to our knowledge, there are no theoretical reports concerning pressure-induced structural phase transitions for BiGaO 3 . Study of high-pressure phases could shed light on physical properties of phases which appear in different solid solutions of BiGaO 3 systems [6][7][8][9][18][19][20]. In addition, in other perovskites, hydrostatic pressure may cause similar effects to chemical doping [21,22].…”