LINK<\/strong><\/a><\/p>\n“LiNbO3-type Mg2.98(2)Al1.99(2)Si3.02(2)O12 (py-LN) was synthesized by recovering a run product from 2000 K and 45 GPa to ambient conditions using a large volume press. Rietveld structural refinements were carried out using the one-dimensional synchrotron XRD pattern collected at ambient conditions. The unit-cell lattice parameters were determined to be a = 4.8194(3) \u00c5, c = 12.6885(8) \u00c5, V = 255.23(3) \u00c53, with Z = 6 (hexagonal, R3c). The average A-O and B-O distances of the AO6 and BO6 octahedra have values similar to those that can be obtained from the sum of the ionic radii of the averaged A- and B-site cations and oxygen (2.073 and 1.833 \u00c5, respectively). The present compound has the B-site cations at the octahedral site largely shifted along the c axis compared with other LiNbO3-type phases formed by back-transition from perovskite (Pv)-structure, and as a result, the coordination number of this site is better described as 3+3. It appears therefore that the B-site cation in the octahedral position cannot be completely preserved during the back-transition because of the small size of Si and Al, which occupy usually a tetrahedral site at ambient conditions. The formation of py-LN can be explained by the tilting of BO6 octahedra of the perovskite structure having the pyrope composition and formed at high P-T conditions. The tilting is driven by the decrease in ionic radius ratio between the A-site cation and oxygen during decompression. This also explains why there is no back-transition from the Pv-structure to the ilmenite-structure during decompression, since this is a reconstructive phase transition whose activation energy cannot be overcome at room temperature. Py-LN may be formed in shocked meteorites by the back-transformation after the garnet-bridgmanite transition, and will indicate shock conditions around 45 GPa and 2000 K.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Takayuki Ishii, Ryosuke Sinmyo, Tetsuya Komabayashi, Tiziana Boffa Ballaran, Takaaki Kawazoe, Nobuyoshi Miyajima, Kei Hirose, Tomoo Katsura American Mineralogist, v. 102, i. 9, p. 1947-1952 First Published on September 05, 2017 doi:10.2138\/am-2017-6027 LINK “LiNbO3-type Mg2.98(2)Al1.99(2)Si3.02(2)O12…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1598,63],"tags":[3631,4184,4183,3176],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/13597"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=13597"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/13597\/revisions"}],"predecessor-version":[{"id":13598,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/13597\/revisions\/13598"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=13597"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=13597"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=13597"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}