Cationic substitution engineering in GdInO3 at A-site: Insights into phase evolution and search for compositionally tailored relaxors

The present work reports detailed structural and electrical studies on A-site substituted LaxGd1-xInO3 (0.0 ≤x ≤ 1.0) system with structurally different end members in search for tailored lead-free relaxors. The motivation is the possibility to manipulate the crystal structure to maneuver electrical properties in hexagonal GdInO3, a candidate for geometric ferroelectricity. The hybrid synthesis protocol involving gel-combustion led to stabilisation of metastable polymorphs in some nominal compositions due to kinetic stabilisation. Non-preference of La3+ for 7- fold coordinated A-site in hexagonal structure manifested in wide-ranging orthorhombic phase field prevailing even in Gd3+-rich region, also supported by theoretical studies. P-E studies on Gd3+-rich compositions exhibited hysteresis loop which suddenly became narrow for the nominal composition La0.4Gd0.6InO3 with very low remanent polarisation. This along with broad maximum exhibited in plot of dielectric constant vs temperature that shifts to higher T upon increasing frequency, for La0.4Gd0.6InO3, supports presence of relaxor-type behavior. Signature of hexagonal-type vibrations in otherwise bulk orthorhombic (by XRD) La0.4Gd0.6InO3 and anomalous trend in La/Gd vibrational mode along with narrowing down of Raman modes have been cited as plausible structural reasons for the relaxor behaviour. This has significance in context of structure-electrical property relationship leading to development of potential lead-free relaxors.