Revised phase diagram of Li2MoO4–ZnMoO4 system, crystal structure and crystal growth of lithium zinc molybdate

Orthorhombic lithium zinc molybdate was first chosen and explored as a candidate for double beta decay experiments with 100Mo. The phase equilibria in the system Li2MoO4–ZnMoO4 were reinvestigated, the intermediate compound Li2Zn2(MoO4)3 of the α-Cu3Fe4(VO4)6 (lyonsite) type was found to be nonstoichiometric: Li2−2xZn2+x(MoO4)3 (0≤x≤0.28) at 600 °C. The eutectic point corresponds to 650 °C and 23 mol% ZnMoO4, the peritectic point is at 885 °C and 67 mol% ZnMoO4. Single crystals of the compound were prepared by spontaneous crystallization from the melts and fluxes. In the structures of four Li2−2xZn2+x(MoO4)3 crystals (x=0; 0.03; 0.21; 0.23), the cationic sites in the face-shared octahedral columns were found to be partially filled and responsible for the compound nonstoichiometry. It was first showed that with increasing the x value and the number of vacancies in M3 site, the average M3–O distance grows and the lithium content in this site decreases almost linearly. Using the low-thermal-gradient Czochralski technique, optically homogeneous large crystals of lithium zinc molybdate were grown and their optical, luminescent and scintillating properties were explored.