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Growth of giant CdWO4 crystals and properties of (010) cleaved surface

Vladimir N. Shlegel 1Victor Atuchin 2Evgeniy N. Galashov 1Lev Pokrovsky 2Aleksandr S. Kozhukhov 2

1. Institute of Inorganic Chemistry of RAS, Novosibirsk 630090, Russian Federation
2. Institute of Semiconductor Physics SB RAS, pr. Lavrentieva 13, Novosibirsk 630090, Russian Federation


Cadmium tungstate, CdWO4, related to family of wolframite-type crystals A2+WO4 is one from the best scintillating mediums. Potentials of this material for laser techniques, acoustics and photocatalytic technologies are under considerations. The parameters of monoclinic cell of CdWO4 : a = 5.0400(8) Å, b = 5.8701(6) Å, c = 5.0841(7) Å, b = 91.476(19)° , V = 150.36(1) Å3, Z = 2, space group P2/c. A chain-type structure is formed by parallel zigzag chains of distorted CdO6 and WO6 octahedrons, spreading along the c axis. The CdWO4 crystals are characterized by good cleavage properties of (010) planes. Micromorphology, structural and electronic properties of CdWO4 (010) cleaved surfaces are evaluated in present study.
High quality inclusion free CdWO4 crystal of 80-90 mm in diameter and of 180-200 mm in length was grown by Low Thermal Gradient Czochralski Technique (LTG Cz). One of the essential features of the LTG Cz technique is the low thermoelastic stresses in the crystal. Respectively, the crystals are less susceptible to post-growth cracking and the dislocation density is much lower in the crystals grown by the LTG Cz technique. The results of CdWO4 crystal growth along the [010] direction are considered in this report. The scintillation and optical properties of 116CdWO4 crystals  grown under the conditions were early reported in Ref. [1]. In practice, the CdWO4 crystal growth along [010] direction is very hard to be realized by conventional high-temperature methods and, as a rule, is not used.
The substrates of CdWO4 (010) with dimensions 12*0.7*12 mm3 were fabricated by accurate cleaving of a single crystal parallelepiped. The top-surface crystallographic properties were evaluated with RHEED  using EFZ4 device at electron energy of 50 keV. The surface micromorphology was studied by AFM with Solver P-47H device. The system of Kikuchi lines are found for cleaved CdWO4 (010) by RHEED that confirms the high crystallographic state of cleaved surface. A substrate surface is formed by a system of wide plane terraces with as low rms as ~0.2 nm and typical area of 3-10 mm2. At the terrace surface the point defects of 15-30 nm in diameter are present. Thermal stability of CdWO4 (010) surface have been traced by annealing in the air over the temperature range of 400-700°C followed by RHEED analysis. High crystallographic quality of cleaved CdWO4 (010) surface gives an opportunity to consider CdWO4 as promising substrate material for epitaxial technologies. There is no foreign phase detected after annealing at 400-600°C. However, the low-intensity precipitation of WO3 and W19O55 oxides was found after annealing at 650-700°C. The epitaxial relations have been obtained for the WO3 and W19O55 precipitates on CdWO4 (010) surface.

1. A.S. Barabash, P. Belli, R. Bernabei, R.S. Boiko, F. Cappella, V. Caracciolo, D.M. Chernyak, R. Cerulli, F.A. Danevich, M.L, Di Vacri, A.E. Dossovitskiy, E.N. Galashov, A. Incicchitti, V.V. Kobychev, S.I. Konovalov, G.P. Kovtun, V.M. Kudovbenko, M. Laubenstein, A.L. Mikhlin, S. Nisi, D.V. Poda, R.B. Podviyanuk, O.G. Polischuk, A.P. Shcherban, V.N. Shlegel, D.A. Solopikhin, Yu.G. Stenin, V.I. Tretyak, V.I. Umatov, Ya.V. Vasiliev and V.D. Virich, Low background detector with enriched 116CdWO4 crystal scintillators to search for double β decay of 116Cd, J. Instrumentation 6 (2011) P08011.


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Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Vladimir N. Shlegel
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-08 10:51
Revised:   2013-04-15 05:56