Synthesis and Structural and Electrical Investigations of a Hexagonal Y_1–xGd_xInO₃ (0.0 ≤ x ≤ 1.0) System Obtained via Metastable C-Type Intermediates

Abstract

Detailed structural and electrical investigations were carried out on an A-site disordered hexagonal Y(1-x)Gd(x)InO3 (0.0 ≤ x ≤ 1.0) series synthesized by a self-assisted gel-combustion route. The phase relations show profound temperature dependence. The metastable C-type modification could be stabilized for all the compositions, which on further heating get converted to stable hexagonal polymorphs. The conversion temperature (C-type to hexagonal) was found to increase with an increase in Y(3+) content. The system was observed to be single-phasic hexagonal at 1250 °C throughout the composition range. Interestingly, the increase in planar bonds of InO5 polyhedra was found to be twice that of the apical bonds on Gd(3+) substitution. Careful Raman spectroscopic studies highlighted a definitive though subtle structural change from x = 0.7 onward. The same observation is also corroborated by the dielectric studies. Electric field-dependent polarization measurements showed the ferroelectric hysteresis loop for pure YInO3. The system transforms from ferroelectric in YInO3 to almost paraelectric for GdInO3. In the present study, XRD, Raman, and electrical characterizations in conjunction reveal that to tune the electrical properties of the hexagonal rare earth indates, the variation in tilting of InO5 polyhedra has to be influenced, which could not be brought about by isovalent A-site substitution.

The role of reaction conditions in the polymorphic control of Eu3+ doped YInO3: structure and size sensitive luminescence

“…5 The appearance of the hexagonal phase at higher temperatures and C-type at lower temperatures is also a significant observation. As has been reported, 14 the tolerance factor (which predicts the structure adopted by the ABO 3 compositions) for YInO 3 is higher than that corresponding to the bixbyite structure and accordingly it should crystallize in the hexagonal structure at room temperature. The stabilization of the metastable C-type phase for YInO 3 can be attributed to the kinetic stability brought about by the nonequilibrium synthesis method adopted here which brings about the randomization of Y and In ions, despite the ionic size difference, favoring the C-type configuration.…”

“…The Raman spectrum of hexagonal YInO 3 has been discussed in our previous work. 14 It must be noted that to the best of our knowledge there has been no detailed Raman analysis of YInO 3 in the literature and the analysis of the Raman spectrum of hexagonal YInO 3 (both in the present work and in ref. 14) has been based on the Raman spectrum exhibited by YMnO 3 which crystallizes in the same space group as YInO 3 and has been investigated by dedicated Raman studies.…”

“…14 It must be noted that to the best of our knowledge there has been no detailed Raman analysis of YInO 3 in the literature and the analysis of the Raman spectrum of hexagonal YInO 3 (both in the present work and in ref. 14) has been based on the Raman spectrum exhibited by YMnO 3 which crystallizes in the same space group as YInO 3 and has been investigated by dedicated Raman studies. 18 It is also noticeable that the same composition of YInO 3 , when adopts the thermodynamically stable modification (which is hexagonal in this case), shows narrower Raman bands which proves the decrease in the strain prevalent in the lattice.…”

Geometrically frustrated GdInO3 : An exotic system to study negative thermal expansion and spin-lattice coupling

“…Unlike the above materials, if B belongs to a non-transition metal ion, the electric or magnetic properties of the system are expected to arise only from the 4f -shell electrons of the rare-earth ion, A. In this regard, rare earth indates, REInO 3 , have emerged as potential candidates for fascinating ferroelectric memory devices [7][8][9][10]. The non-centrosymmetric atomic arrangement in the hexagonal unit cell of this system gives rise to the geometric ferroelectricity [11].…”

First principles study of ferroelectric hexagonal compounds RInO3(R = Dy, Er, and Ho): electronic structure, optical and dielectric properties

“…Among the ABO 3 perovskite structures, RMnO 3 (R ¼ rare-earth element) has been widely studied due to its excellent ferroelectric and dielectric properties, [7][8][9][10][11][12][13] and hexagonal RInO 3 with the space group of P6 3 cm is isomorphic to the hexagonal RMnO 3 . 14 If we replace Mn 3+ ions with non-transition metal In 3+ ions, the dielectric and optical properties of the RInO 3 perovskite system are only contributed by the 4f-shell electrons of the rare-earth ions R 3+ , [15][16][17][18][19][20][21] which makes it much more straightforward to study the optical and dielectric properties of RInO 3 than in RMnO 3 . Studies have shown that the spontaneous polarization of hexagonal RInO 3 increases with the increase of the atomic number of rare-earth elements.…”