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–xGd_xInO₃ (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 Y³⁺ 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 Gd³⁺ 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.