Mechanochemical Synthesis of Nonstoichiometric Nanocrystals
La_{1 y}Ca_yF_{3 y} with a Tysonite Structure and Nanoceramic
Materials from CaF₂ and LaF₃ Crystals

B. P. Sobolev^a, I. A. Sviridov^b, V. I. Fadeeva^b, S. N. Sul’yanov^a, N. I. Sorokin^a,
Z. I. Zhmurova^a, I. I. Khodos^c, A. S. Avilov^a, and M. A. Zaporozhets^a

^a Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninski pr. 59, Moscow, 119333 Russia

e-mail: fluorides@ns.crys.ras.ru

^b Faculty of Chemistry, Moscow State University, Moscow, 119992 Russia

^c Institute of Microelectronics Technology and High-Purity Materials, Russian Academy of Sciences, Institutskaya ul. 6,
Chernogolovka, Moscow oblast, 142432 Russia

Received January 18, 2008

Abstract—The nonstoichiometric phases La_1yCa_yF_3y (y = 0.15, 0.20) with a tysonite (LaF₃) structure have
been prepared for the first time by the mechanochemical synthesis from CaF₂ and LaF₃ crystals. The average
size of coherent scattering regions is approximately equal to 10–30 nm. It has been shown that the com-
positions of the phases prepared by the mechanochemical synthesis are inconsistent with the phase dia-
gram of the CaF₂LaF₃ system. The “mechanohydrolysis” of the La_1yCa_yF_3y phase has been observed for
the first time. Under these conditions, the La_1yCa_yF_3y phase partially transforms into lanthanum calcium
oxyfluoride for a milling time of 180 min with intermediate sampling. The La_1yCa_yF_3y nanoceramic mate-
rials have been prepared from a powder of the mechanochemical synthesis product by pressing under a pressure
of (2–6) 10⁸ Pa at room temperature. The electrical conductivity of the synthesized materials at a temperature
of 200C is equal to 4.9(6) 10⁴ S/cm, and the activation energy of electrical conduction is 0.46(2) eV. These
data for the nanoceramic materials coincide with those obtained for migration of fluorine vacancies in single-
crystal tysonite fluoride materials.

PACS numbers: 64.75.Jk, 61.46.-w

DOI: 10.1134/S1063774508050234

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