ISSN:
1600-5767
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Geosciences
,
Physics
Notes:
The d33 piezoelectric coefficient in sodium oxonium trihydroxotrioxoiodate (2−) is 4.3 ± 0.5 × 10−12 CN−1 at 298 K. The p3 pyroelectric coefficient is 4.3 ± 0.3 × 10−6 Cm−2 K−1 at 298 K, increasing to 14.5 × 10−6 Cm−2 K−1 at 220 K and becoming zero at about 137 K; p3 changes sign at lower temperatures. The absolute sense of the two coefficients at 298 K, determined with respect to the atomic arrangement, is given by d33〉0, p3 〈0. The Na+ ions are embedded within layers of I(OH)3O32− ions: the H3O+ ions are attached to these anion layers by strong hydrogen bonds. Compressive stress equivalent to finger pressure on a 1 mm2 crystal face displaces the Na+ ions toward the OH− surfaces and the H3O+ ions toward the O− surfaces of the anion layer by about 10−4 Å. An increase in temperature of 100 K displaces the positive ions in the same sense by about 2 × 10−3 Å. A similar model for elbaite tourmaline predicts an average cation displacement of 5–10 × 10−4 Å along the polar axis, on cooling the crystal through 100 K, consistent with the recent results of G. Donnay [Acta Cryst. (1977), A33, 927–932].
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0021889879011869
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