The atomic structures of single crystals of the sillenites Bil2(Bio.5oFeo.5o)Olg.5o and Bi12(Bi0.67Zno.

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Thermal atomic vibrations in the cubic phase of Cs,NaNdCI, single crystal undergoing the structural phase transition (PT) at 138 K are investigated from the data of X-ray diffraction obtained at 278, 218, and 148 K. A significant anisotropy of thermal vibrations and their deviations from harmonic behaviour are found for the C1-atoms of the structure. These atoms displace from their equilibrium positions below PT due t o the tilts of the octahedral groups. 218 M 148 K , MccneAoBaH xapamep TennoBbix x o n e 6 a~a l a-roMoB B ~y 6 w i e c~o t j aa3e no PeHTTeHOBCKMM AM@paKUMOHHblM AaHHbIM, nOJly4eHHbIM ITPI4 TeMnepaTypaX 278, KpMCTanna Cs,NaNdCI,, KOTOpbIt npM 138 K MCnbITbIBaeT C T P J W T Y P H M~~ Qa30BbIt nt?peXOn;. YCTaHOBneHbI CyUeCTBeHHafi aHEI30TpOnM23 M OTKJIOHeHI4H OT rBpMOHHqecxoro 3 a~o~a B TennoBHx KOne6aHUfiX aToMoB C1, KoTopMe B npouecce @aao~oro nepexona cMeWaloTcR 143 CBOUX nonomemi4 3a CY&T ~O B O~O T O B C B~~H H~I X O K T~~A P M -gecKHx rpynn. I) 660036 Krasnoyarsk, USSR.

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