Effect of Mg doping on the growth aspects, crystalline perfection, and optical and thermal properties of congruent LiNbO₃single crystals

Abstract

Mg-doped congruent lithium niobate single crystals were grown by the Czochralski technique. High-quality single crystals were grown using a novel seeding technique in a resistive heating furnace. Analysis of crystalline perfection carried out by a multi-crystal X-ray diffractometer revealed that the grown crystals do not contain any structural grain boundaries but do contain point defects. The transmission characteristics showed an enhancement of band gap with an increase in Mg concentration. Conoscopy patterns revealed that the grown crystals are homogeneous and the incorporation of Mg into the lattice does not affect the optical sign (negative uniaxial) of the crystal. The refractive index measurements carried out using a prism coupler showed an increase in the optical birefringence (Án), while the refractive index was found to decrease with the increase in doping concentration. Further, thermal conductivity was found to decrease with Mg incorporation in the lattice owing to phonon scattering from the Mg ions and, as a consequence, at high concentrations (> 4 mol%) crack formation occurred. However, optimization of growth conditions reveals that a slower pulling rate leads to crack-free lithium niobate crystals even at 6 mol% Mg doping.

Control of Intrinsic Defects in Lithium Niobate Single Crystal for Optoelectronic Applications

“…Figure 11 also shows the variation of both the n o and n e for Mg:CLN in comparison to that of undoped CLN. A gradual decrease of n o and n e with the increase in the Mg doping concentration was noticed, which is attributed to the decrease in the concentration of intrinsic defects of Nb Li 5+ in CLN due to Mg doping [70]. It shows that Mg ions influence the microscopic polarizability and dielectric susceptibility of CLN for both the polarizations.…”

“…A multi-step synthesis route was adopted as described in ref. [70]. An indigenously developed automatic diameter controlling software was used to grow crystals with uniform diameter.…”

“…However, the growth of crystals with 6 mol % Mg using the same growth conditions resulted in cracking due to excess strain because of the higher concentration of Mg. However, a low pulling rate of 1 mm/h and slow post-growth cooling of 50 • C/h led to crack-free 6 mol % Mg-doped crystals [70]. The typical sizes of the grown crystals were~25 mm in diameter and 30-40 mm in length ( Figure 2).…”

“…The chemical was synthesized as per the procedure reported in ref. [70]. The axial temperature gradient of the furnace used was ~10 °C/cm.…”

Electro‐Optic Property of Mg2+/Er3+‐Codoped LiNbO3 Crystal: Mg2+ Concentration Threshold Effect

“…The constant WDS signals indicate that the Mg and Er elements are homogeneous enough over the whole sample plate. Indeed, some effective measures can ensure to grow large crystal with high optical quality and homogeneity …”