Dielectric constants of BaO and melilites and the oxide additivity rule
Shannon, Robert D.; Iishi, Kazuaki; Allik, Toomas H.; Liebertz, Josef; Rossman, George R.
European Journal of Mineralogy Volume 4 Number 6 (1992), p. 1241 - 1250
published: Dec 15, 1992
manuscript accepted: Feb 27, 1992
manuscript received: Nov 18, 1991
ArtNo. ESP147050406022, Price: 29.00 €
Abstract The constant-stress "free" dielectric constants and dissipation factors of BaO and a series of X2YZ2O7 melilites were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: BaO κ = 31.1 Ca2MgSi2O7 κTa = 11.83 κTc = 7.97 Ca2CoSi2O7 κTa = 12.44 κTc = 9.00 Ca2ZnSi2O7 κTa = 12.03 κTc = 8.21 Sr2CoSi2O7 κTa = 8.93 κTc = 6.87 Ba2MgGe2O7:Nd,Ce κTa = 8.75 κTc= 7.51 The discrepancies between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to αD(X2YZ2O7) = 2 αD(XO) + αD(YO) + 2 αD(ZO2) are + 13.6 to + 16.0% for Ca-containing melilites, + 6.1% for Sr2CoSi2O7 and + 1.0% for Ba1.92Nd0.04Ce0.04MgGe2O7. The deviations from additivity in the Ca- and Sr-melilites are believed to result from structural misfit between the alkaline earth X ion and the YZ2O7 layers which leads to rattling X ions.