  Sm$_2$Ti$_2$O$_7$, a member of rare-earth titanate pyrochlores, exhibits
dipolar-octupolar antiferromagnetism below $T_N$ = 0.35 K. We observed two
ferroelectric transitions at 182 ($T_{FE1}$) and 52 K ($T_{FE2}$),
significantly higher than $T_N$ for Sm$_2$Ti$_{2-x}$V$_x$O$_7$ ($x$ = 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 $Fd\bar{3}m$
structure occurs at $T_{FE1}$, 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.
