Wurtzite Oxynitrides

Another series of oxynitrides which, in contrast to most of the preceding nitrogen-rich compounds, has more or less equal amounts of the two nonmetals is the M Si202N2 series, where M is a divalent cation (typically Ca, Sr, or Ba) [43]. All of these compounds are monoclinic, and would appear to be essentially point compositions. 

No data have yet been reported on the further substitution of Al—O in place of Si—N, even though this would be expected to a limited extent. Studies conducted by 

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Gray NaGe2N3 [80] and the white oxynitrides NaGeON and NaSiON form with a wurtzite superstructure [81]. NaGe2N3 was the first example of Na in a fully nitrided environment. The structures are similar to those of the corresponding Li compounds. 

In addition to the P-SiAlON phase, a number of other phases have also been observed in this system [18, 20] including X-phase, so-called because its stmcture was unknown O, i.e., silicon oxynitride with partial replacement of Si and N by A1 and O and six phases with ranges of homogeneity extending along lines of constant M X ratio between P and AIN. The phases based on a wurtzite-type stmcture have been characterised as polytypoids related to AIN [23]. The stmctures... 

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