High-temperature X-ray investigation of natural columbites |
| |
| Authors: | S C?Tarantino Email author" target="_blank">M?ZemaEmail author M?Pistorino M C?Domeneghetti |
| |
| Institution: | (1) Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy |
| |
| Abstract: | Structural investigations at high temperature were carried out on natural columbite samples across the join Fe(Nb0.95Ta0.05)2O6–Mn(Nb0.95Ta0.05)2O6. The samples were preliminarily annealed to attain the complete cation-ordered state and avoid the superimposition of the effects of cation ordering during high-temperature studies. Unit-cell parameters of three columbites with different XFe content were measured at regular intervals in the temperature range 25–900 °C using single-crystal X-ray diffraction techniques. The crystal structures of completely ordered ferrocolumbite and manganocolumbite were also refined from intensity data collected at room temperature, 300 and 600 °C. Structural thermal expansion coefficients show positive, linear expansion of a, b, c lattice constants and cell volume. In general, slightly higher expansion occurs along a and c directions. However, anisotropy decreases sharply with decreasing Fe content. Reversibility of thermal expansion in the investigated temperature range was checked by high-temperature diffraction studies under heating-up and cooling-down conditions. Impurities do not play an important role in thermal expansion of columbites; expansion coefficients measured on two crystals of the same sample characterized by different Ti content are in fact almost identical. Structural changes with temperature essentially affect bond lengths: volumes of both A and B octahedral sites increase linearly with temperature, whereas interpolyhedral geometrical parameters do not vary significantly. |
| |
| Keywords: | Columbite HT X-ray diffraction Thermal expansion |
| 本文献已被 SpringerLink 等数据库收录！ |
|
