Experimental and numerical investigations of the Czochralski growth of Li2MoO4 crystals for heat-scintillation cryogenic bolometers

Abstract

A new technology for the mass production of lithium molybdate (Li2MoO4) crystals needed for the realization of the cryogenic neutrinoless double-beta decay detectors is under development within the framework of the CLYMENE project. Crystals with 4 and 5 cm in diameter were grown in two different Czochralski configurations. The first configuration, based on inductive heating of a RF coil coupled with a platinum crucible, was used to grow crystals of 4 cm in diameter. Bolometric tests performed with two samples cut from a 230 g crystal have shown less performances of the large sample (158 g), which had a cleavage, as compared to the small non-cracked sample (13.5 g). Numerical 2 modeling was applied to investigate the temperature field in the furnace, the melt convection and thermo-elastic stresses in the crystal. Numerical results reveal 30% higher thermal stress at the bottom part of the ingot in the case of a concave shape of the crystal tail (experimental case) as compared to the case of a convex shaped tail. This could explain why the fracture started at the bottom part of the 230 g crystal boule, and highlights the importance of the crystal shape in the last stage of growth process. The furnace configuration used to grow 5 cm-diameter crystals was numerically optimized in order to reduce the thermal stress in the crystals. The first kg-mass Li2MoO4 ingot grown in the optimized configuration exhibit regular shape and good structural quality.

Test of 116CdWO4 and Li2MoO4 scintillating bolometers in the CROSS underground facility with upgraded detector suspension

“…Another crystal scintillator studied in the present work is Li 2 MoO 4 , which was developed within the R&D program of the CLYMENE project [24,25,[32][33][34]. The optimization of the Cz growth process was guided by COMSOL multiphysics modeling and numerical simulations in conjunction with well-chosen experimental validations [34].…”

“…The optimization of the Cz growth process was guided by COMSOL multiphysics modeling and numerical simulations in conjunction with well-chosen experimental validations [34]. The furnace configuration and the crystal growth parameters were optimized to produce large-volume ingots with a regular shape (5 cm in diameter, about 15 cm in length) and with reduced thermal stresses [25,32,33], in contrast to the first large CLYMENE crystal (0.23 kg) which exhibited a partial cleavage starting from the bottom part of the ingot [24]. Two parts of this crystal with [24] and without [35] a cleavage were tested as low-temperature scintillating detectors, particularly showing the impact of the crystal crack on the phonon propagation.…”

Conventional Czochralski growth of large Li2MoO4 single crystals

“…In order to understand the origin of this crack better, stresses occurring during growth have been calculated by finite element numerical simulation of heat transfer and thermo-elasticity, by the Comsol ® software. The modelling procedure is the same as presented in [21,22],…”

“…Therefore, a more classical Czochralski process, provided that too high temperatures are avoided, could be a less expensive, more productive technique for the growth of high quality Li 2 MoO 4 crystals. In preceding papers [21,22], numerical simulation was used for optimizing the hot zone of a Czochralski furnace in order to prevent melt overheating or undercooling, avoid large stresses in the crystal and provide a slightly convex solid-liquid interface (seen from the melt). Based on this approach, the growth of several crystals is described.…”

Scintillation in Low-Temperature Particle Detectors

“…The results achieved with the advanced Li 2 MoO 4 cryogenic scintillator [311] triggered an extensive R&D on Li 2 MoO 4 scintillating bolometers recently realized within the ISOTTA and LUMINEU projects [74,345,[475][476][477]. Currently, several R&D activities on the Li 2 MoO 4 development for scintillating bolometers are ongoing world-wide: in France (CLYMENE project [478][479][480][481]), in the Republic of Korea [482][483][484][485], in China [486,487], in the United States [488,489], in Ukraine [490], in addition to the existing crystal growth technologies in Russia [74,311,473,476,[491][492][493][494]. Most of these activities were and are considered part of R&D programs towards large-scale bolometric DBD search experiments CUPID [82,495,496] and AMoRE [81,483].…”