Structural (at room temperature) and dielectric and thermal properties of TlH2AsO4 have been studied as functions of temperature to understand the existence of its reported phase transition. The space group and cell parameters of the compound were determined. The crystal structure was determined by Patterson and Fourier difference methods and refined by the full-matrix least-squares technique. The structure can be explained in terms of zig-zag chains of H-bonds running along thec-axis. Careful studies on dielectric and thermal properties of the substance do not suggest any ferroelectric phase transitions in it.
