dielectric constants of olivine

Dielectric Constants of Tephroite, Fayalite and Olivine and the Oxide Additivity Rule

R.D. Shannon, M.A. Subramanian

E. I. Du Pont de Nemours and Co., Inc., Central Research and Development Department,
Experimental Station, Wilmington, DE 19880-0356, U.S.A.

S. Hosoya

Institute for Materials Research, Tohoku University, Katsura 2-1-1
Sendai 980, Japan

G.R. ROSSMAN

Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 91125-2500, U.S.A

Abstract

The dielectric constants ad dissipation facctors of synthetic tephroite (Mn₂SiO₄), fayalite (Fe₂SiO₄) and a forsteritic olivine (Mg_1.80Fe_0.22SiO₄) were measured at 1 MHz using a two-terminal method and empiriclly determined edge corrections. The results are:

tephroite
κ'a = 8.79
κ'b = 10.20
κ'c = 8.94

fayalite
κ'a = 8.80
κ'b = 8.92
κ'c = 8.58

olivine
κ'a = 7.16
κ'b = 7.61
κ'c = 7.03

tan δa = 0.0006
tan δb = 0.0006
tan δc = 0.0008

tan δa = 0.0004
tan δb = 0.0018
tan δc = 0.0010

tan δa = 0.0006
tan δb = 0.0008
tan δc = 0.0006

The low dielectric constant and loss of the fayalite indicate an exceptionally low Fe³⁺ content. An FeO polarizability of 4.18 Å³, determined from a_D(FeO) = [a_D(Fe₂SiO₄) - a_D(SiO₂)]/2, is probably a more reliable value for stoichiometric FeO than could be obtained from Fe_xO where x = 0.90-0.95. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to a_D(M₂M'X₄) = 2a_D(MX) + a_D(M'X₂) is ~ +2.8% for tephroite and + 0.2% for olivine. The deviation from additivity in tephroite is discussed.

Phys Chem Minerals (1991) 18:1-6