AbstractThe temperature dependences of the refractive indices n
j(t) and the values <n(t)> = (n
|| + 2n
⊥)/3,
n
(t) =
ε
-1/2,
ε
= (ε
|| + 2ε
⊥)/3, ε
j = n
j2 for the light waves polarized along (j = ||) and across (j = ⊥) the director in uniaxial calamitic liquid crystals (LCs) were studied within the microscopic approach with taking into account the anisotropy of the local-field tensor f
j(t) =1 + L
j(t)[ε
j(t)–1] and the Lorentz tensor L
j(t). The known negative derivatives <n(t)>' = d<n(t)>/dt,
n
' and the point t
o of minimum at the dependence n
⊥(t) for calamite LCs were shown to correspond to small and medium values of the birefringence Δn = n
|| – n
⊥. For LCs with high values of δn and components L
⊥ exceeding the threshold value L
⊥e two new effects were predicted: positive derivatives <n>', and the presence of the point t
e of maximum at the dependence n
||(t). For a number of nematics with high values of Δn the components L
j(t) were determined, the presence of the predicted effects and the conditions for their manifestation were confirmed, the values
te were obtained and their connection with the magnitude Δn were established. The features of the transition from LCs with point to t
o LCs with point c under gradual increase in Δn were cleared up.
Keywords: liquid crystals, temperature dependences of the refractive indices
