This paper reports on the development of a technology involving 100 Mo-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed nextgeneration bolometric experiment to search for neutrinoless double-beta decay. Large mass (∼ 1 kg), high optical quality, radiopure 100 Mo-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2-0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the doublebeta transition of 100 Mo (3034 keV) is 4-6 keV FWHM. The rejection of the α-induced dominant background above 2.6 MeV is better than 8σ . Less than 10 µBq/kg activity of 232 Th ( 228 Th) and 226 Ra in the crystals is ensured by boule recrystallization. The potential of 100 Mo-enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only 10 kg×d exposure: the two neutrino double-beta decay half-life of 100 Mo has been measured with the up-to-date highest accuracy as T 1/2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] × 10 18 years. Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of 100 Mo.

Large lithium molybdate (Li 2 MoO 4 ) crystal boules were produced by using the low thermal gradient Czochralski growth technique from deeply purified molybdenum. A small sample from one of the boules was preliminary characterized in terms of Xray-induced and thermally-excited luminescence. A large cylindrical crystalline element (with a size of ⊘40 × 40 mm) was used to fabricate a scintillating bolometer, which was operated aboveground at ∼ 15 mK by using a pulse-tube cryostat housing a highpower dilution refrigerator. The excellent detector performance in terms of energy resolution and α background suppression along with preliminary positive indications on the radiopurity of this material show the potentiality of Li 2 MoO 4 scintillating bolometers for low-counting experiment to search for neutrinoless double beta decay of 100 Mo.

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Synthesis and X-Ray Diffraction Study of Potassium, Rubidium, and Cesium Polytungstates with Defect Pyrochlore and Hexagonal Tungsten Bronze Structures.-X-ray studies on the phase formation in M 2 WO 4 -WO 3 systems (M: K, Rb, Cs) verify the formation ofCs 6 W 11 O 36 and the existence of M 4 W 11 O 35 and M 2 W 7 O 22 phases. M 2 W 3 O 10 and Cs 6 W 11 O 36 possess a pyrochlore type structure whilst the structure of M 4 W 11 O 35 and M 2 W 7 O 22 resembles hexagonal tungsten bronze. Appropriate conditions for the solid phase synthesis and crystallization of discrete polytungtates from the corresponding alkali carbonate M 2 CO 3 and WO 3 are established. -(SOLODOVNIKOV, S. F.; IVANNIKOVA, N. V.; SOLODOVNIKOVA, Z. A.; ZOLOTOVA, E. S.; Neorg.