The (1x)BiFeO 3 -xLaFeO 3 system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3c phase is observed for 0.0 e x e 0.10. The PbZrO 3 -related ffiffi ffi p 2a p  2 ffiffi ffi p 2a p  4a p superstructure (where a p is the parameter of the cubic perovskite subcell) is observed for Bi 0.82 La 0.18 FeO 3 , while an incommensurately modulated phase is formed for 0.19 e x e 0.30 with the ffiffi ffi p 2a p  2a p  ffiffi ffi p 2a p basic unit cell. The GdFeO 3 -type phase with space group Pnma ( ffiffi ffi p 2a p  2a p  ffiffi ffi p 2a p ) is stable at 0.50 e x e 1. Bi 0.82 La 0.18 FeO 3 has no detectable homogeneity range (space group Pnam, a=5.6004(1) A ˚, b=11.2493(3) A ˚, c=15.6179(3) A ˚).The incommensurately modulated Bi 0.75 La 0.25 FeO 3 structure was solved from synchrotron X-ray powder diffraction data (Imma(00γ)s00 superspace group, a = 5.5956(1) A ˚, b = 7.8171(1) A ˚, c = 5.62055(8) A ˚, q=0.4855(4)c*, R P =0.023, R wP =0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A=Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the antipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO 3 -type structure at high temperatures. Bi 0.82 La 0.18 FeO 3 shows an intermediate PbZrO 3 -type phase with ffiffi ffi p 2a p  2 ffiffi ffi p 2a p  2a p (space group Pbam; a = 5.6154(2) A ˚, b = 11.2710(4) A ˚, and c = 7.8248(2) A ˚at 570 K). The compounds in the compositional range of 0.18 e x e 0.95 are canted antiferromagnets.

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.

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Solid solutions InMn(1-x)Ga(x)O(3) (0 ≤ x ≤ 1) have been investigated using magnetic, dielectric, specific heat, differential scanning calorimetry (DSC), and high-temperature powder synchrotron X-ray diffraction (HT-SXRD) measurements. It was found that samples with 0.5 ≤ x ≤ 1 crystallize in space group P6(3)/mmc with a ~ 3.32 Å and c ~ 11.9 Å, and samples with 0.0 ≤ x ≤ 0.4 crystallize in space group P6(3)cm with a ~ 5.8 Å and c ~ 11.6 Å at room temperature. HT-SXRD data revealed the existence of a P6(3)cm-to-P6(3)/mmc phase transition at about 480 K in InMn(0.6)Ga(0.4)O(3) and at 950 K in InMn(0.7)Ga(0.3)O(3). However, no dielectric, phonon, second-harmonic-generation, or DSC anomalies were found to be associated with these phase transitions. The phase transition should be improper ferroelectric from the symmetry point of view, but the above-mentioned experimental facts, together with the absence of ferroelectric hysteresis loops, revealed no evidence for ferroelectricity in the low-temperature P6(3)cm structure. We suggest that InMn(1-x)Ga(x)O(3) corresponds to a nonferroelectric phase of hexagonal RMnO(3) with P6(3)cm symmetry. The antiferromagnetic phase-transition temperature decreases from 118 K for x = 0 to 105 K for x = 0.1 and 73 K for x = 0.2, and no long-range magnetic ordering could be found for x ≥ 0.3. Specific heat anomalies associated with short-range magnetic ordering were observed for 0.0 ≤ x ≤ 0.5. InMn(1-x)Ga(x)O(3) with small Mn contents (0.8 ≤ x ≤ 0.98) has a bright-blue color.