High-pressure behavior of NaInSi2O6 and the influence of Me3+ on the compressibility of NaMe3+Si2O6 silicates

The equation of state of a single-crystal synthetic silicate NaInSi2O6 was determined from the unit cell parameters measured by X-ray diffraction using a diamond-anvil cell at 12 different pressures up to 7.83(1) GPa in order to provide a definitive model capable of predicting the high-pressure behavior of NaMe3 +Si2O6 silicate compounds. The P – V data were fitted by a third-order Birch–Murnaghan equation of state obtaining the following coefficients: V 0 = 463.42 ( 3 ) Å 3 , K T 0 = 109.0 ( 6 ) GPa , K ′ = 3.3 ( 2 ) . Our results show similar results for NaMe3 +Si2O6 compounds and confirm that for this mineral family, the empirical K T 0 × V 0 = constant relationship proposed in previous investigations is valid for isostructural compounds only if they share the same valence electron character. In addition, we collected intensity data on the same compound at 16 different pressures up to 9.467 GPa using a diamond-anvil cell with diamond backing plates. The main structural compression mechanism is played by the tetrahedral chain kinking, which is related to the shortening of Na–O3long distances. ing our equation of state and high-pressure crystal structural results with previous data on NaMe3 +Si2O6 pyroxenes, we show that their compressibility increases much faster with the size of Me3 + cation when this one is a 3d transition metal.