Science. 1978 Jan 27;199(4327):422-5. doi: 10.1126/science.199.4327.422.
The existence of a cubic fluorite-type SnO(2) and a hexagonal TiO(2) (which may be related to the fluorite structure) have been demonstrated by an in situ x-ray diffraction study in which a diamond-anvil pressure cell was used after the samples had been heated by a continuous yttrium-aluminum-garnet laser. At room temperature, the lattice parameter for SnO(2) (fluorite) is a = 4.925 +/- 0.005 angstroms and those for TiO(2) (fluorite-related) are a = 9.22 +/- 0.01 angstroms and c = 5.685 +/- 0.006 angstroms at about 250 kilobars. The volume change associated with the transition from rutile to fluorite (or related structure) is about -8 percent for SnO(2) and -10.5 percent for TiO(2) at transition. Upon release of pressure, both the fluorite-type SnO(2) and the TiO(2) reverted to the alpha-PbO(2) structure at room temperature. The hypothesis that the earth's lower mantle is composed of oxide phases might be feasible if it were possible for SiO(2) to possess the fluorite structure or its related forms at high pressure, as shown for SnO(2) and TiO(2) in this study. The oxide hypothesis proposed here differs from that postulated by Birch in that the primary coordination of silicon is 6 for Birch's hypothesis and 8 for the hypothesis presented here.
在使用金刚石压腔进行原位 X 射线衍射研究中，加热样品后，用连续掺钇铝石榴石激光照射，证明存在立方萤石型 SnO(2)和六方金红石型 TiO(2)（可能与萤石结构有关）。在室温下，SnO(2)（萤石型）的晶格参数为 a = 4.925 +/- 0.005 埃，TiO(2)（与萤石有关的）的晶格参数为 a = 9.22 +/- 0.01 埃和 c = 5.685 +/- 0.006 埃，约为 250 千巴。SnO(2)从金红石向萤石（或相关结构）转变的体积变化约为-8%，TiO(2)为-10.5%。在减压过程中，室温下，两种萤石型 SnO(2)和 TiO(2)都恢复到α-PbO(2)结构。如果 SiO(2)在高压下具有萤石结构或其相关形式，如本研究中 SnO(2)和 TiO(2)所示，那么地球下地幔由氧化物相组成的假设可能是可行的。这里提出的氧化物假设与 Birch 的假设不同，因为硅的一级配位数对于 Birch 的假设是 6，而对于这里提出的假设是 8。
