Tl²⁺ EPR detection of glassy behavior in ADP_x - RDP_1−x and deuteration effects in the phase diagram of AD_x⁻ RDA_1−x

Abstract

Using the large (≈ 100 GHz) hyperfine coupling of the Tl²⁺ (6s¹) ion as a spin probe, we have investigated the evolution of glassy behavior in (NH₄) _xRb_1−xH₂ PO₄ single crystals. Also reported is a microwave dielectric loss determination of the phase diagram of (ND₄) _xRb_1−xD₂AsO₄. The glass formation temperature, T_c, is found to be significantly higher and the glass phase range narrower in the deuterated arsenate system than in the corresponding protonated arsenate system. Both of these phenomena are tentatively interpreted in terms of a random bond version of the Ising model in a transverse tunneling field.