Structural Evolution and Properties of Solid Solutions of Hexagonal InMnO₃ and InGaO₃

Abstract

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.

Observation of persistent centrosymmetricity in the hexagonal manganite family

“…9 However, in contrast to the case of the ferroelectric manganites, the structure refinements of the XRD data reveals equally good fits for the centrosymmetric space group P3c and the noncentrosymmetric space group P6 3 cm 14 consistent with a previous observation. 9 In Table I we report our refined atomic co- ordinates and lattice parameters within the P3c and P6 3 cm space groups. In general, structures refined with the correct space group are lower in energy than those refined with incorrect space groups.…”

“…11 In agreement with this, Belik et al did not observe spontaneous polariza-tion when they repeated the experiment. 7,9 Therefore there is no clear evidence to date that InMnO 3 has the P6 3 cm structure or shows ferroelectric polarization.…”

“…1) -and polar P6 3 cm structure have similar powder x-ray-diffraction R values. 9 They disregarded the P3c model in their subsequent analysis, however, believing that all h-RMnO 3 compounds should be polar. Indeed, ferroelectricity has been reported in InMnO 3 below 500 K based on the observation of polarization-electric field (P-E) hysteresis loops obtained by a ferroelectric test system.…”

Phase segregation in Mn-doped In2O3: in situ high-pressure high-temperature synchrotron studies in multi-anvil assemblies

“…It is worthy of note that o-InOOH was also observed as a side phase in a recent synthesis of InMnO 3 and In-Mn-Fe-O perovskites as well as corundum-type In 222x Zn x Sn x O 3 oxides performed at 6 GPa/ 1100-1500 uC and 7 GPa/1000 uC, respectively. [26][27][28] Hence, the appearance of o-InOOH under high-pressure high-temperature…”

“…It is worthy of note that o-InOOH was also observed as a side phase in a recent synthesis of InMnO 3 and In-Mn-Fe-O perovskites as well as corundum-type In 222x Zn x Sn x O 3 oxides performed at 6 GPa/ 1100-1500 uC and 7 GPa/1000 uC, respectively. [26][27][28] Hence, the appearance of o-InOOH under high-pressure high-temperature conditions in indium-containing specimens can be an issue for the synthesis of binary and ternary indium oxides and requires further, more careful, study. The scanning electron micrographs (Fig.…”