The Pressure-Induced Local Structural Change Around Tungsten In Silicate Glass

Tungsten is one of the key elements to understand the conditions and timing of planetary core formation. While the metal-silicate partitioning of tungsten has been extensively studied, the effects of pressure and silicate melt composition have been controversial. Here we have investigated the local environment of tungsten in a basaltic glass up to 67 GPa based on EXAFS spectroscopy and found that the W-O bond length increases in a pressure range from 10 to 32 GPa, indicating that W6+ ion increases the coordination number from four to six. It is known that the coordination of silicon also changes at similar pressure range, suggesting that the coordination structure of trace element tungsten may be controlled by the Si-O coordination. The coordination change of tungsten will affect its metal-silicate partitioning and may explain the previously observed change in the pressure effect around 5 GPa, when considering the difference between melt and glass. This also suggests further change in the pressure dependence above 32 GPa where tungsten is predominantly sixfold coordinated. In addition, the effect of silicate melt composition may diminish at such pressure range.