Elastic properties of the dithionates Na₂S₂O₆ · 2 H₂O, K₂S₂O₆, Rb₂S₂O₆, CaS₂O₆ · 4H₂O and SrS₂O₆ · 4 H₂O

Abstract

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 K2S2O6 and Rb2S2O6, which is screened by a hexagonal hypermorphy, could be clearly revealed to be trigonal (32) by the existence of the elastic constant c14. In the case of CaS2O6 · 4H2O and SrS2O6 · 4H2O the constant c14 of the specimens appeared too small to confirm the trigonal symmetry group required from electrooptic and non‐linear optic effects unambiguously. The isotypy of K2S2O2 and Rb2S2O6 as well as that of CaS2O6 · 4H2O and SrS2O6 · 4H2O 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 K2S2O6 near 235 K weak anomalies of the temperature derivatives of the longitudinal elastic stiffnesses are observed.

Calcium dithionate tetrahydrate, CaS2O6⋅4H2O, a novel SRS-active crystal for octave-spanning many-phonon Stokes and anti-Stokes combs

“…The crystals of CaS 2 O 6 •4H 2 O appear trigonal (3m or 32) and often also hexagonal (6m or 6/mm). Their twinning is clearly visible from striations on faces of rhombohedra of type {30h 3 } [11]. The striations run parallel to the edges formed by these faces with {001} [11] (see figure 1(a)).…”

“…Their twinning is clearly visible from striations on faces of rhombohedra of type {30h 3 } [11]. The striations run parallel to the edges formed by these faces with {001} [11] (see figure 1(a)). Besides these fine striations, rough disturbances by reentrant angles are often observed [11].…”

“…The striations run parallel to the edges formed by these faces with {001} [11] (see figure 1(a)). Besides these fine striations, rough disturbances by reentrant angles are often observed [11]. The twinning plane is (001).…”

“…For the description of the physical properties, a Cartesian reference system was introduced with basis vectors e i , which are related to the crystallographic basis vectors a i according to e 1 a 1 , e 3 a 3 , and e 2 = (e 1 × e 3 ). The hexagonal lattice parameters a 1 = 6.211(2) Å, a 2 = 6.211(1) Å, a 3 = 18.763(2) Å, α 1 = α 2 = 90 • , α 3 = 120 • were reported from x-ray diffraction experiments [11]. In order to clarify the space group of Ca 2 S 2 O 6 •4H 2 O at 293 K, single-crystal x-ray diffraction experiments were performed at room temperature with a four-circle diffractometer (Xcalibur from Oxford Diffraction) equipped with graphite-monochromatized Mo Kα-radiation and a CCD camera.…”

“…Optionally, radiation at the third harmonic wavelength λ f3 = 0.354 72 µm can be generated using a subsequent KD 2 PO 4 (DKDP) crystal. Due to the sum frequency mixing process (λ f1 + λ f2 = λ f3 ) we assume that the pulse duration is approximately the same as for the 3m Formula units per unit cell Z = 3 Density measured (g cm −3 ) [11] d m = 2.180 Dehydration (4H 2 O) [12] 353-398 K Decomposition (SO 2 ) [12] 533-593 K Nonlinearity χ (2) + χ (3) Optical transparency range (µm) b ≈0.21-≈1.85 (see figure 2) Thermal expansion (10 −6 K −1 ) [11] α 11 = 44(2); α 33 = 0(1) Elastic constants (10 [31]. b For a ≈ 7-mm thick crystal along (102) direction.…”