期刊
PHYSICS AND CHEMISTRY OF MINERALS
卷 34, 期 4, 页码 215-221出版社
SPRINGER
DOI: 10.1007/s00269-006-0140-8
关键词
barium carbonate; phase transformation; equation of state; high pressure; diamond anvil cell
Barium carbonate (BaCO3) was examined in a diamond anvil cell up to a pressure of 73 GPa using an in situ angle-dispersive X-ray diffraction technique. Three new phases of BaCO3 were observed at pressures > 10 GPa. From 10 to 24 GPa, BaCO3-IV had a post-aragonite structure with space group Pmmn. There are two molecules in a single unit cell (Z = 2) of the orthorhombic phase, which is same as the high-pressure phases of CaCO3 and SrCO3. The isothermal bulk modulus of BaCO3-IV is K (0) = 84(4) GPa, with V-0 = 129.0(7)A(3)(degrees) over bar when K (0)'= 4. The c axis of the unit cell parameter is less compressible than the a and b axes. The relative change in volume that accompanies the transformation between BaCO3-III and BaCO3-IV is similar to 6%. BaCO3-V, which has an orthorhombic symmetry, was synthesized at 50 GPa. As the pressure increases, BaCO3-V is transformed into tetragonal BaCO3-VI. This transformation is likely to be second order, because the diffraction pattern of BaCO3-V is similar to that of BaCO3-VI, and some single peaks in BaCO3-VI become doublets in BaCO3-V. After decompression, the new high-pressure phases transform into BaCO3-II. Our findings resolve a dispute regarding the stable high-pressure phases of BaCO3.
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