An Arrhenius plot of the conductivity revealed 2 or 3 transition points at -25 and/or -52C and -108C. Heat capacity measurements clearly indicated 3 peaks: at -27, -52 and -107C. The suggestion that there were 3 transition points was confirmed by positron annihilation experiments. The ionic conductance of both porous and dense specimens was measured between -80 and 80C under hydrostatic pressures of between 0.5 and 1.6kbar. A conductivity maximum appeared close to 4 to 5kbar on the conductance versus pressure curves of porous specimens. The conductance decreased with increasing pressure in the case of dense specimens. The activation volumes were equal to 0.90 and 1.55cm3/mol for the α-phase and the β-phase, respectively.

L.Chen, Z.Zhao, R.Xue, G.Wang: Solid State Ionics, 1983, 9-10,1223-6