Low-temperature XRD study of ferroelectric phase transition and enhanced magnetodielectric effect in Tb1− <i>x</i> In <i>x</i> MnO3

This study investigates the structural, dielectric, and magnetodielectric properties of indium-doped TbMnO3 (Tb1−xInxMnO3, x = 0.00, 0.05, 0.075) synthesized via the solid-state method. Low-temperature x-ray diffraction (XRD) measurements reveal a temperature-driven phase transition from the centrosymmetric orthorhombic Pnma space group at 300 K to the non-centrosymmetric Pna21 space group at 11 K, indicative of ferroelectric behavior. Below the transition temperature, sudden changes in lattice parameters, unit cell volume, Mn–O bond lengths, and Mn–O–Mn bond angles with varying temperature may be associated with spin–lattice coupling that underlies magnetoelectric behavior. The optical bandgap, as estimated from UV–visible absorption spectra, slightly decreases with In3+ substitution. This experimental observation is well supported by DFT + U calculations. Dielectric and magnetodielectric measurements confirm ferroelectric transitions at ∼22 ± 0.5, 20 ± 0.5, and 20 ± 0.5 K for x = 0.00, 0.05, and 0.075, respectively. An enhanced magnetodielectric effect is observed with In doping, peaking at 3.49% for x = 0.05 under a 5 T magnetic field. The findings highlight the role of non-magnetic A-site doping in tuning the multiferroic behavior of TbMnO3, making it a promising candidate for multifunctional device applications.