Temperature and baric changes in the refractive indices of LiKSO4 crystals

Structure and refractive properties of LiNaSO4 single crystals

“…It is worth noting that LSS reveals a rather high optical anisotropy as for the crystals of ABSO 4 group, with only (NH 4 ) 2 SO 4 and β-LiNH 4 SO 4 having still higher anisotropy. A comparison of the birefringence values found for LSS and LiKSO 4 at 500 nm [17] demonstrates that the Δn parameter of LSS (0.0064) is more than order of magnitude larger than that of LiKSO 4 (0.0006). Perhaps, the only possible explanation of this great difference is notably different second-anion coordination environments of LiNaSO 4 and LiKSO 4 (see Section 3).…”

“…A comparison of the refractive parameters of LSS with those peculiar to LiKSO 4 [17,28] shows that the cationic substitution K → Na leads to a slight decrease in the electronic polarizability (~ 7%) and molar refractivity (~ 13%), a displacement of the ultraviolet-oscillator position towards shorter wavelengths (~ 26 nm), and an increase of the B parameter associated with the oscillator strength (~ 10% and ~ 25% for the x and z axes). Notice also that the refractivity parameters R for LiRbSO 4 and, especially, α-LiNH 4 SO 4 are essentially (~ 50%) larger than that of LSS (see Refs.…”

“…Nonetheless, the cationic substitution K → Na leads to nearly twice as large increase in the refractive indices, if compared with the substitutions K → Rb and K → NH 4 (see discussions in Refs. [17][18][19]). Fig.…”

“…As far as we know, there is no data concerned with these characteristics, except for the refractive indices for a single wavelength (~ 589.3 nm) and a mention that LSS is optically uniaxial [4]. Among different aspects, an interest to the optical anisotropy is due to the fact that the ABSO 4 -group crystals often reveal inversion of sign of the optical birefringence, or simply 'isotropic point' [17][18][19][20]. The latter is interesting from the fundamental point of view [21,22] and, moreover, finds its applications in a number of practical fields [23][24][25].…”

“…The latter is interesting from the fundamental point of view [21,22] and, moreover, finds its applications in a number of practical fields [23][24][25]. Since the isotropic point has been observed in structurally close LiKSO 4 crystals [17], it would be interesting to consider the effect of cation substitution on the optical anisotropy and examine the presence of the phenomenon in LiNaSO 4 .…”