Laevorotatory Bi12SiO20crystallizes in the cubic system with space group 123 anda=10.10433plusmn;0.00005 Aring; at 298 K. The integrated intensities of 5488 reflections within a hemisphere of reciprocal space with (sinVthgr;/ggr;quest;1.15 Aring;minus;Lwere measured with monochromatic MoKagr; radiation. A total of 977 independent and significantly nonzeroFmeaswere used to determine the crystal structure by the method of least squares. The final agreement factorR=0.0316. The Sindash;O distance within the geometrically regular SiO4tetrahedron is 1.647plusmn;0.005 Aring;. The Bindash;O bond distances, ranging from 2.064plusmn;0.009 to 2.647plusmn;0.003 Aring;, with two additional contacts of 3.06 and 3.161 Aring; formed by the Bi inert 6s2electron pair are all within 0.025 Aring; of the corresponding distances Bi12GeO2. The absolute sense of the piezoelectricd14coefficient is such that tensile stress along lsqb;111rsqb; generates positive polarity on (111), the face toward which the oxygen apex of the SiO4tetrahedra points,i.e.,d1450. The magnitude ofd14was determined in a static experiment to be 37.8plusmn;2.0x10minus;12CNminus;1.
展开▼
