Structural relation of phase A to ringwoodite: predicted possible low-pressure polymorph of Mg7Si2H6O14 (phase AII) derived as recombination structure from forsterite

A possible low-pressure polymorph of Mg7Si2H6O14 (phase AII) was derived from forsterite as a recombination structure. The present study suggests that phase A, high-pressure polymorph of Mg7Si2H6O14, can be regarded as one member of a homologous series of hypothetical post-humite high-pressure phases derived from ringwoodite as a parent structure. This implies the possible significance of post-humite high-pressure phases whose stability field might be close to phase A as candidates for the hosts of water in the mantle.