Electrical relaxation in double doped calcium fluoride and activation volume for the RI relaxation J. J. Fontanella, R. J. Kimble, Jr., M. C. Wintersgill, C. Andeen and M. K. Smith J. Phys. Colloques, 41 C6 (1980) C6-458-C6-461 DOI: 10.1051/jphyscol:19806119