The structure and elasticity of phase B silicates under high pressure by first principles simulation**Project supported by the Science Fund from the Key Laboratory of Earthquake Prediction, Institute of Earthquake Science, China Earthquake Administration (Grant No. 2016IES010104) and the National Natural Science Foundation of China (Grant Nos. 41174071, 41273073, 41373060, and 41573121).

Abstract

The structures and elasticities of phase B silicates with different water and iron (Fe) content are obtained by first-principles simulation to understand the effects of water and Fe on their properties under high pressure. The lattice constants a and b decrease with increasing water content. On the contrary, c increases with increasing water content. On the other hand, the b and c decrease with increasing Fe content while a increases with increasing Fe content. The decrease of M (metal)–O octahedral volume is greater than the decrease of SiO polyhedral volume over the same pressure range. The density, bulk modulus and shear modulus of phase B increase with increasing Fe content and decrease with increasing water content. The compressional wave velocity (Vp) and shear wave velocity (Vs) of phase B decrease with increasing water and Fe content. The comparisons of density and wave velocity between phase B silicate and the Earth typical structure provide the evidence for understanding the formation of the X-discontinuity zone of the mantle.