Original paper

High-temperature ferroelastic strain below the I2/c-I1 transition in Ca1-xSrxAl2Si2O8 feldspars

McGuinn, Martin D.; Redfern, Simon A. T.

European Journal of Mineralogy Volume 9 Number 6 (1997), p. 1159 - 1172

29 references

published: Dec 2, 1997
manuscript accepted: May 22, 1997
manuscript received: Aug 20, 1996

DOI: 10.1127/ejm/9/6/1159

BibTeX file

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Abstract Lattice parameters of feldspars of composition Ca1-xSrxAl2Si2O8, {x = 0.85, 0.80, and 0.75) have been measured as a function of temperature (T) from room-T to 950 °C. At room-T each is triclihic (I1), undergoing a continuous ferroelastic displacive transition to a monoclinic phase (I2/c) on heating. The observed critical temperature (Tc) increases as Ca content increases. The thermodynamic character of the transition also changes, from near-second-order at x = 0.85, approaching tricritical as Ca content increases. Curvature of the transition line through composition (X)-T space suggests the importance of high-order coupling between X and the order parameter. Strain-tails in cc and γ close to Tc are interpreted in terms of inhomogeneity of the M-cation distribution, related to tweed microstructures noted in previous investigations. A Landau model is derived which describes the observed transition-related phenomena in the system Ca1-xSr8Al2Si2O8 as a function of T and X.


Ca-Sr feldsparshigh-temperature X-ray diffractionphase transitionferroelasticityLandau theory