Polymorphic Behavior of Titania under Dynamic Loading

Journal of Chemical Physics - Tập 50 Số 1 - Trang 319-325 - 1969
Ronald K. Linde1, Paul S. DeCarli1
1Poulter Laboratory for High Pressure Research, Stanford Research Institute, Menlo Park, California 94025

Tóm tắt

Single-crystal and polycrystalline specimens (including powder compacts of various densities) of titanium dioxide have been subjected to shock-wave pressures in the 150–1000–kbar range. Hugoniot measurements have disclosed a phase transition commencing below 200 kbar, and x-ray diffraction studies of specimens recovered after shocking to various pressures above 150 kbar have shown the presence of an orthorhombic phase with the α-PbO2 structure. Calculated lattice parameters are a = 4.55 Å, b = 5.46 Å, and c = 4.92 Å, which correspond to a crystal density of 4.34 g/cm3. The orthorhombic phase appears to result on release of pressure from a considerably denser phase of TiO2 (postulated to have approximately 8:4 oxygen-titanium coordination) that dynamic measurements indicate is formed under shock. Yields of the α-PbO2 phase as high as about 90% have been obtained from [001]- and [111]-oriented rutile crystals shocked to 450 kbar. At atmospheric pressure this phase can be retained indefinitely at temperatures below 340°C, but reverts to rutile rapidly at 550°C. An activation energy of 66 ± 5 kcal/g-mole has been computed for reversion of specimens containing predominantly the orthorhombic phase but also containing some nuclei of rutile. The average crystallite size of shocked material is typically as small as 100–200 Å, and crystallites obtained from initially single-crystal rutile exhibit preferred orientation. Shocked specimens of rutile and of the orthorhombic phase have ESR spectra that exhibit surface-sensitive behavior, but which do not appear to be dependent upon the relative amounts of rutile and orthorhombic phase present. Petrographic and electron microscopy observations of shocked material are also reported.

Từ khóa


Tài liệu tham khảo

1966, Solid State Phys., 19, 229

1966, J. Appl. Phys., 37, 3259, 10.1063/1.1703192

1958, Solid State Phys., 6, 1, 10.1016/S0081-1947(08)60724-9

1968, Science, 161, 893, 10.1126/science.161.3844.893

1967, Science, 155, 1401, 10.1126/science.155.3768.1401

1966, Geokhimiya, 5, 499

1968, Trans. Am. Geophys. Union, 49, 310

1965, Zh. Eksp. Teor. Fiz., 49, 1728

1966, Sov. Phys.-JETP, 22, 1181

1967, Science, 158, 388, 10.1126/science.158.3799.388

Thông tin
Thông tin xuất bản

Journal of Chemical Physics

Tập 50 Số 1

319-325

Thông tin tác giả