Single-crystal X-ray diffraction structural data of four Fe-Mg tourmalines with different Fe contents from Xinjiang, Sichuan, and Yunnan Provinces, China, were collected at room temperature and-100oC. The intrinsic dipole moments of polyhedra and the total intrinsic dipole moment of the unit cell were calculated. By comparing the intrinsic electric dipole moments of the X, Y, Z, T, and B site polyhedra, it is found that the T site polyhedron makes the greatest contribution to the total intrinsic dipole moment. The pyroelectric coefficients of four Fe-Mg tourmalines were experimentally determined, and the influence of intrinsic dipole moments on their pyroelectric properties was investigated. The experimental results show that, compared with the case at room temperature, the intrinsic dipole moments change with the total Fe content at-100oC in a completely different way. With the decrease of temperature, the total intrinsic dipole moments of tourmaline decrease. Over the same temperature interval, the pyroelectric coefficients increase with the increase in intrinsic dipole moment.
We studied four tourmalines with different Fe contents from Xinjiang,Sichuan,and Yunnan provinces of China using M ssbauer spectroscopy and single crystal X-ray diffraction.The valence and location of Fe in the four tourmalines and two heat-treated tourmalines have been investigated.The experimental results showed that Fe in the four tourmalines at room temperature had two valence states and two locations,i.e.Fe2+(Y),Fe2+(Z),Fe3+(Y).After being heated at 850℃ for 48 and 72 h,Fe elements in tourmaline were nearly completely oxidized and mainly occupied Y sites,and a small amount of Fe3+ shifted to Z sites.Simultaneously,the amount of mixed valence state Fe 2.5+ progressively increased with heating time,and electron delocalization occurred between the adjacent sites [Fe2+-Fe3+].
