Pressure variation of C1 NQR in hexachlorostannate crystals

The effect of hydrostatic pressure (0 < p < kbar) on the ³⁵Cl NQR in K₂SnCl₆, (NH₄)₂SnCl₆, Rb₂SnCl₆ and Cs₂SnCl₆ was studied in the temperature range 20 K to 450 K. In the cubic phase the linear pressure coefficients of the NQR frequency ν_Q are negative. The frequency shifts are discussed in the scope of a microscopic model considering the variation of the static and dynamic part of the electric field gradient (EFG).On applying pressure the relaxation rate T₁^?1 decreases. At elevated temperature this pressure behaviour is attributed to the increase of the enthalpy of activation of the SnCl₆^2? motion. For K₂SnCl₆ the volume of activation ΔV_a could be estimated from the T₁^?1(P,T) data. Using this value a barrier height to rotation of ΔE_a = 4800 K is obtained.