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Elastic properties of the dithionates Na 2 S 2 O 6 · 2 H 2 O, K 2 S 2 O 6 , Rb 2 S 2 O 6 , CaS 2 O 6 · 4H 2 O and SrS 2 O 6 · 4 H 2 O
Author(s) -
Haussühl S.
Publication year - 1994
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170290126
Subject(s) - thermoelastic damping , trigonal crystal system , hexagonal crystal system , crystallography , chemistry , symmetry (geometry) , stiffness , order (exchange) , condensed matter physics , materials science , physics , thermodynamics , geometry , crystal structure , mathematics , thermal , finance , economics
Single crystals of the title compounds having optical quality and dimensions of several cm were grown from aqueous solutions. The elastic and thermoelastic constants were determined from ultrasonic resonance frequencies of thick plates. The true point symmetry of K 2 S 2 O 6 and Rb 2 S 2 O 6 , which is screened by a hexagonal hypermorphy, could be clearly revealed to be trigonal (32) by the existence of the elastic constant c 14 . In the case of CaS 2 O 6 · 4H 2 O and SrS 2 O 6 · 4H 2 O the constant c 14 of the specimens appeared too small to confirm the trigonal symmetry group required from electrooptic and non‐linear optic effects unambiguously. The isotypy of K 2 S 2 O 2 and Rb 2 S 2 O 6 as well as that of CaS 2 O 6 · 4H 2 O and SrS 2 O 6 · 4H 2 O is confirmed by their elastic behaviour. The mean elastic stiffness of dithionates is closely related to that of the corresponding sulphates. In the vicinity of the second‐order phase transition of K 2 S 2 O 6 near 235 K weak anomalies of the temperature derivatives of the longitudinal elastic stiffnesses are observed.