Successive ferroelectric orders and magnetoelectric coupling without long-range magnetic order in highly frustrated pyrochlore compounds. Sm2⁢Ti(2−𝑥)⁢V𝑥⁢O7

Sm2Ti2O7, a member of the 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 with V doping. A structural transition to a polar R3m rhombohedral phase from the cubic Fd3m structure occurs at TFE1 for the pristine compound, involving a distortion in the pyrochlore lattices formed by the Sm atoms. Remarkably, linear magnetoelectric coupling is observed in both compounds, with further enhancement of magnetoelectric (ME) coupling due to magnetic V doping. The existence of magnetoelectric coupling without long-range magnetic order is of fundamental interest for advancing the understanding and development of ME coupling.