Composition effect on electro-optic (EO) properties of a LiNbO₃ (LN) single-crystal has been investigated in a Li₂O-content range of 47.0–49.95 mol%. Some non-congruent LN crystals with different Li₂O-contents were prepared by performing Li-deficient or Li-rich vapour transport equilibration treatments on as-grown congruent LN crystals. Unclamped EO coefficients γ₁₃ and γ₃₃ of these samples were measured by a Mach–Zehnder interferometric method. The measurements show that in the Li-deficient regime both γ13 and γ33 increase by ∼8% as Li₂O-content decreases from the congruent 48.6 mol% to the 47.0 mol% in the Li-deficient regime. The feature is desired for the EO application of the Li-deficient crystal. In the near-stoichiometric regime, both γ₁₃ and γ₃₃ reveal a non-monotonic dependence. As the Li₂O-content increases from the 48.6 mol%, the EO coefficient decreases. Around Li₂O-content 49.5 mol%, a minimum is reached. After that, the EO coefficient recovers slowly. At the stoichiometric composition, it recovers to a value close to that at the congruent point. Comparison shows that different crystal growth methods give rise to different defect structure features and hence different composition effects.

Photoactive nanofilled nematic is proposed. Stable three-component photoresponsive nanocomposite was prepared from photo-insensitive nanofilled nematic by inclusion of 3 wt.% azobenzene-containing photoactive mesogen 4-(4′-ethoxyphenylazo)phenyl hexanoate (EPH). The host nanofilled nematic was produced from the room-temperature nematic liquid crystal 4-n-heptyl cyanobiphenyl (7CB) and 3 wt.% filler of Aerosil 300 hydrophilic silica nanospheres of size 7 nm. Apparent effect of stimulation with a relatively weak continuous illumination by UV light (375 nm wavelength) takes place for both the alternating-current electric field-dependent optical transmittance and the electro-optic amplitude-frequency modulation by thin films (25 µm thick) of the EPH/aerosil/7CB nanocomposite. The light-stimulated electro-optics of EPH-doped aerosil/7CB films and the corresponding reversible light control are achieved through trans-cis-trans photoisomerization of the photoactive agent EPH. As such, the initial electro-optical response of the studied photoactive nanocomposites is recovered with continuous blue-light illumination. The examined EPH/aerosil/7CB nanocomposites exhibit photo-controllable electro-optical response that is of practical interest.