Single-crystal NMR for the layered semiconductor TlGaSe₂

We report on a ⁶⁹Ga and ²⁰⁵Tl NMR study of single-crystal thallium gallium selenide. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T_c = 107.5 to T_i = 118K. On approaching phase transition at T_i from above, the crystal exhibits soft mode behavior, which is somewhat different for thallium and gallium substructures. Redistribution of ⁶⁹Ga line intensities with temperature in the ferroelectric phase indicates a variation of the domain structure of this phase.