Crystal structure of moganite-type phosphorus oxynitride: relationship to other twinned-quartz-based structures

The structure of moganite-type phosphorus oxynitride quenched from high-pre ssure high-temperature conditions has been refined using neutron powder dif fraction data. This moganite-type structure, space group I2/a, Z = 12. is s lightly less distorted with respect to the Imab aristotype than is moganite (a monoclinic form of silica). A close topological relationship has been i dentified between the moganite-type and orthorhombic BeH2 structures indica ting that SiO2, PON and BeH2 all adopt structures belonging to the twinned- quartz-based group. This group represents another possible structure type f or systems composed of corner-sharing AX(4) tetrahedra. Structures of this group are obvious candidates for intermediate phases between the cristobali te and quartz types.