Dielectric constants of BaO and melilites and the oxide additivity rule
Abstract
The constant-stress "free" dielectric constants and dissipation factors of BaO and a series of X_2YZ_2O_7 melilites were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: BaO K = 31.1 Ca_2MgSi_2O_7 K^T_a = 11.83 K^T_c = 7.97 Ca_2CoSi_2O_7 K^T_a = 12.44 K^T_c = 9.00 Ca_2ZnSi_2O_7 K^T_a = 12.03 K^T_c = 8.21 Sr_2CoSi_2O_7 K^T_a = 8.93 K^T_c = 6.87 Ba_2MgGe_2O_7:Nd,Ce = K^T_a = K^T_c= 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 ɑ_D(X_2YZ_2O_7) = 2 ɑ_D(XO) + ɑ_D(YO) + 2 α_D(Z0_2) are + 13.6 to + 16.0% for Ca-containing melilites, + 6.1% for Sr_2CoSi_2O_7 and + 1.0% for Ba_(1.92)Nd_(0.04)Ce_(0.04)MgGe_2O_7. 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 YZ_2O_7 layers which leads to rattling X ions.
Additional Information
© 1992 E. Schweizerbart'sche Verlagsbuchhandlung. Received 18 November 1991. Accepted 27 February 1992. We thank R.W. Shiffer for sample preparation, R.A. Oswald for making the capacitance measurements, M.A. Subramanian for helpful discussions, L.F. Lardear and R.H. Harlow for crystal orientation and single crystal data from BaO, C. Foris for Guinier photographs and obtaining cell dimensions, and J.T. Armstrong (California Inst. Technology, Pasadena, CA) for microprobe data. This work was supported in part by National Science Foundation Grant EAR-86-18200.Additional details
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- 38233
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- CaltechAUTHORS:20130502-102431085
- EAR-86-18200
- NSF
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2013-05-02Created from EPrint's datestamp field
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2019-10-03Created from EPrint's last_modified field
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- Division of Geological and Planetary Sciences