NUCLEAR-QUADRUPOLE DOUBLE-RESONANCE STUDY OF RBH2PO4 IN THE SUPERCOOLED HIGH-TEMPERATURE MONOCLINIC PHASE

Rubidium nuclear-quadrupole-resonance (NQR) spectra have been measured in the high-temperature monoclinic phase of RbH2PO4 above T(p) = 86-d egrees-C and also in the supercooled high-temperature phase below T(p) . At the transition into the high-temperature phase, the rubidium quad rupole-coupling constants drop by a factor of 5. The high-temperature phase is metastable below T(p). The kinetics of the transformation of the metastable phase into the stable tetragonal phase in a polycrystal line sample is determined at room temperature from the time dependence of the rubidium NQR spectra. A comparison of the present rubidium NQR data in the high-temperature monoclinic RbH2PO4 with the rubidium NQR data in monoclinic RbD2PO4 suggests that at low temperatures, superco oled monoclinic RbH2PO4 may be isostructural with the phase III of mon oclinic RbD2PO4 whereas above T(p) RbH2PO4 may be isostructural with p hase II of RbD2PO4.