Compression Studies of Single-Crystal SnO2 and PbO2 in a Diamond Cell

單晶SnO2及PbO2之鑽石砧壓研究

黃怡禎(Eugene Huang)；李淑玲(Alice S. Li)；余樹楨(Shu-Cheng Yu)

Terrestrial, Atmospheric and Oceanic Sciences

3卷2期（1992 / 06 / 01）

111 - 127

英文

本實驗藉鑽石高壓砧對兩金紅石結構之單晶雙氧化物，錫石(SnO2, cassiterite)及塊黑鉛礦(PbO2, plattnerite)進行常溫之壓縮研究，樣本置於靜水壓狀態，其所受之壓力經由紅寶石螢光測壓法量出。利用四環單晶繞射儀以收集繞射資料。錫石在被加壓到35仟粑(kbar)之過程中，其結構仍保持不變，只有晶格常數c/a之比值隨壓力增高而變大，其彈性模量(bulk modulus)定為2.24±0.08百萬粑(Mbar)。塊黑鉛礦則在5仟粑時由正方晶系轉變為斜方晶系。轉變後之斜方相之三軸呈現不同之壓縮係數。由於在相轉變時摩耳體積之改變並無不連續之現象推測該斜方相為由金紅石(β-PbO2)轉變為α-PbO2之過渡相。塊黑鉛礦之彈性模量可定為1.34±0.06百萬粑，綜合上述結果與其它資料，發現在金紅石結構之單晶雙氧化物內，其整體聲速(bulk sound velocity)和平均原子量(mean atomic weight)間有線性關係存在。

Compression behaviors of two single-crystal rutile-structure dioxides, SnO2 (cassiterite) and PbO2 (plattnerite), were studied in a Merrill-Bassett type diamond cell at room temperature. The samples were compressed in a mixture of 4:1 methanolethenol solution with pressure measurements by the ruby scale. A four-circle diffractometer was used to obtain the diffraction patterns of these crystals at high pressures. Compression results on Sn02 did not show significant lattice distortion, with a slight increase in c/a up to 35 kbar. The compression data are in excellent agreement with Hazen and Finger (1981) and in reasonable agreement with Ming and Manghnani (1982). Fitting these data to the Birch-Murnaghan equation gives a bulk modulus (K。) of 2.24±0.08 Mbar with K。' =6.3. On the other hand, the rutile-type PbO2 was found to transform from a tetragonal to an orthorhombic phase above 5 kbar. The cell parameters a, b and c of this phase have different linear compressibility. This phase is different from the reported orthorhombic phases of lead dioxides (α-PbO2). It could represent an intermediate distorted phase which occurs during the transformation from the β-PbO2 to the α-PbO2 phase. The bulk modulus of Pb02 was determined to be 1.34±0.06 Mbar by fitting the data to the Birch-Murnaghan equation. A linear relationship was found to exist between the bulk sound velocity and mean atomic weight of the rutile-type dioxides.