The electric-field gradient (EFG) of dilute ¹¹¹Cd nuclei in compounds of the Hg-In alloy system has been investigated by perturbed angular correlation (PAC) measurements of the electric quadrupole interaction (QI) of ¹¹¹Cd on In sites. It has been found that, as in the pure metals Hg and In, the quadrupole frequency decreases with increasing temperature according to the relation nu _q(T)= nu _q(0)(1-BT³2/). The strength constant B in the intermetallic phases, however, is up to 35% smaller than in the pure metals. The QI parameters are consistent with an orthorhombic gamma -Pu-type lattice for beta -Hg (Hg₈₀In₂₀), but are difficult to reconcile with the structures proposed for HgIn. An intermetallic compound HgIn₂ has not been observed.