The temperature (T) and pressure (P) dependence of dielectric and conductivity properties of natural leucite were determined using complex impedance spectroscopy at frequencies from 103 to 106 Hz. Experiments were carried out in a Walker multi-anvil cell at 1 atm and P from 2.5 to 6 GPa and at T from 350 to 800°C. At pressure >6 GPa and temperature >790°C the leucite broke down to kalsilite+sanidine and dielectric properties for this phase assemblage are given at 6.0–7.0 GPa and T to 1050°C.

Leucite conductivity increases with increasing T and decreases with increasing P reflecting their different effects on migration of K cations within the channels in the leucite aluminosilicate framework. Activation energies for K+ migration in leucite increase with increasing pressure (0.74–0.97 eV; 70.0–93.2 kJ/mol) and activation volumes for leucite increase with increasing T (6.42–9.51 cm3/mol; 400–700°C). The latter data provide model K+ cation diameters increasing from 2.7 Å at 400°C to 3.2 Å at 700°C. These values are consistent with the earlier suggestion of Palmer and Salje that the ionic mobility mechanism consists of diffusion along <110> rather than along the main channels parallel to <111>.

Pure Cu was made ultrafine-grained by equal channel angular pressing on route BC at ambient temperatures and deformed in situ in a scanning electron microscope at the elevated temperature of 373 K and at a constant total strain rate of 10−4 s−1. Deformation was repetitively stopped to take micrographs of the grain structure on the same area of observation, revealing limited activity of discontinuous dynamic recrystallization. During the stops of deformation, the flow stress was relaxing. The relaxation of stress as function of time was used to determine the rate of inelastic deformation as a function of stress, from which the activation volume ${V^ * }$ of the thermally activated flow was derived. It is found that the normalized values of ${V^ * }$ were lying in the same order generally found for coarse-grained pure materials. This seems to be in conflict with the literature. However, the conflict is resolved by noting that the literature results refer to quasistationary deformation with the concurrent dynamic recovery in contrast to the present results obtained at a virtually constant microstructure. The interpretation of the two kinds of activation volumes for thermally activated flow is discussed.