Abstract
The complex dielectric constant of Tl(H1−X DX)2AsO4 powder pellets has been measured from 100 to 450 K. It is found that the I11 ← 11 phase transition point (TL) shifts from 251 K(for hydrogenated crystal) to about 340 K(for partially deuterated crystal), while the I1 ← I phase transition point(TU) goes from about 390 K to 433 K. The order of the I11 ← I1 phase transition changes from a weakly first-order to a second- order, while that of the I1 ← I phase transition from a second-order to a first-order. From the experimental results, the tentative phase diagrams of Tl(H1−X DX)2AsO4, and Tl(H1−X DX)2PO4 are proposed.