Sodium polymolybdates grown by low-thermal-gradient Czochralski technique for scintillating applications

Presented work is dedicated to the search of new perspective scintillating materials for rare events physics, particularly neutrinoless double beta-decay projects. Such implementations imposes strict requirements on scintillator quality and radioactive background. Most bivalent cations have radioactive isotopes, thus, light alkali cations are better fitted for this purpose. Moreover, due to their small ionic radii Li and Na are less substituted by U and Th.

Another issue with obtaining crystals for scintillation purposes is the minimal working size of the element – 40*40 mm³ while maintaining uniformity in entire bulk volume. We propose the low-thermal-gradient Czochralski technique (LTG Cz) developed at NIIC SB RAS as a unique technology for obtaining bulk oxide crystals of high optical quality. Temperature gradients in LTG Cz compared to the conventional Czochralski technique are two orders of magnitude lower, ​​less than 1 deg/cm.

In literature several versions of Na₂O-MoO₃ phase diagrams are presented, stating stable compounds Na₂MoO₄, Na₂Mo₂O₇, Na2Mo4O13 (impossible for obtaining because of polymorphic phase transition) and in different works Na₄Mo₉O₂₉, Na₆Mo₁₀O₃₃, Na₆Mo₁₁O₃₆. Space group of the compound Na₆Mo₁₁O₃₆ was determined on powder samples as triclinic. In presented work, Na_xMo_yO_z crystals were grown by LTG Cz technique. Space group of Na₆Mo₁₁O₃₆ crystal sample was determined as monoclinic.

Acknowledgements

This work was supported by the Russian Science Foundation № 23-23-10068 and Novosibirsk Region Grant № p-49 (https://rscf.ru/project/23-23-10068).