Successive ferroelectric orders and magnetoelectric coupling without long-range magnetic order in highly frustrated pyrochlore compounds: Sm₂Ti₂₋ₓVₓO₇

Sm₂Ti₂O₇, a member of rare-earth titanate pyrochlores, exhibits dipolar-octupolar antiferromagnetism below TN = 0.35 K. We observed two ferroelectric transitions at 182 (TFE1) and 52 K (TFE2), significantly higher than TN for Sm₂Ti₂₋ₓVₓO₇ (x = 0, 0.1). Although the ferroelectric transition temperatures remain unchanged, the polarization value decreases considerably with V doping. A structural transition to a polar $R3m$ rhombohedral phase from the cubic Fd3̄m structure occurs at TFE1, involving a distortion in the pyochlore lattice. Remarkably, significant linear magnetoelectric coupling is observed in both compounds, with further enhancement of magnetoelectric coupling due to magnetic V doping. The existence of magnetoelectric coupling without long-range magnetic order in a frustrated pyrochlore system could enable the tailoring of magnetoelectric coupling properties, which can be further fine-tuned through V doping. The emergence of ferroelectricity in a frustrated magnetic system introduces an intriguing aspect to these compounds and paves the way for developing ferroelectric order driven by the alleviation of magnetic frustration in pyrochlore systems.