Feldspars crystallized in the range SrF80An20-SrF60An40 of the join CaAl2Si2O8-SrAl2Si2O8 from gels at T = 1350-1500-degrees-C for short time show cell parameters significantly different from those obtained from longer heating. This difference has been interpreted as due to higher metastable Al/Si disorder in short heated samples and to more ordered configurations with longer heat treatments. HT powder spectra show that the T(c) of the I1BAR-I2/c phase transition of feldspars changes with composition and with the degree of order at constant composition; the evolution of the spontaneous strain (approximately cosalpha*) versus T for the samples examined shows a variation in the order of the transition from continuous (II order) in more ordered and Sr-rich samples to a discontinuous behaviour (presumably I order) for more disordered and Sr-poor samples. A biquadratic coupling between displacive and OD parameters is therefore suggested.
I(1)over-bar-i2/c Phase-transition In Alkaline-earth Feldspars Along the Caal2si2o8-sral2si2o8 Join - Thermodynamic Behavior / Tribaudino, Mario; P., Benna; E., Bruno. - In: PHYSICS AND CHEMISTRY OF MINERALS. - ISSN 0342-1791. - 20:(1993), pp. 221-227.
I(1)over-bar-i2/c Phase-transition In Alkaline-earth Feldspars Along the Caal2si2o8-sral2si2o8 Join - Thermodynamic Behavior
TRIBAUDINO, Mario;
1993-01-01
Abstract
Feldspars crystallized in the range SrF80An20-SrF60An40 of the join CaAl2Si2O8-SrAl2Si2O8 from gels at T = 1350-1500-degrees-C for short time show cell parameters significantly different from those obtained from longer heating. This difference has been interpreted as due to higher metastable Al/Si disorder in short heated samples and to more ordered configurations with longer heat treatments. HT powder spectra show that the T(c) of the I1BAR-I2/c phase transition of feldspars changes with composition and with the degree of order at constant composition; the evolution of the spontaneous strain (approximately cosalpha*) versus T for the samples examined shows a variation in the order of the transition from continuous (II order) in more ordered and Sr-rich samples to a discontinuous behaviour (presumably I order) for more disordered and Sr-poor samples. A biquadratic coupling between displacive and OD parameters is therefore suggested.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
