Novikova M.S.1,
Bagautdinov B.Sh2,
Aleksandrova I.P.3,
Blomberg M.4
1Institute of
Crystallography RAS, Moscow, mashanov@crystal.ras.msk.su
2 Institute of Solid State
Physics, RAS, Chernogolovka, bagautdi@issp.ac.ru
3Institute of Physics, CD
RAS, Krasnoyarsk, aleks@iph.krasnoyarsk.su
4Helsinki
University, Finland, blomberg@rock.helsinki.fi
Keywords: modulated phases, phase transitions, x-ray study, A3B2X9 family
The crystal Cs3Sb2I9 at room temperature is characterized by P-3m1 with lattice parameters a= 8.45, c=10.34 A and belongs to the family A3B2X9[1]. Many compounds of this family show phase transitions at cooling. The existence of phase transition (T1=86 K and T2=72 K) in Cs3Sb2I9 is found using NMR and other methods [2].
In the present work X--ray refinment of this compound at T = 294 K was made up to R = 0.04. Study of the reciprocal space on 4-circle diffractometer "Huber" showed the appearance of satellites at low temperature on (hl) and (kl) planes .. Also X-Ray study of the low temperature PTs using "Siemens-500" diffractometer adapted for monocrystal studies with low-temperature equipment was carried out.
The X-Ray shows that the PT at 88K is connected with doubling the lattice period along c-axis.
The second PT at T2 is connected with the
appearance of satellites (h k+1/2 l+1/2). In the temperature
range 78K -72K these satellites show the incommensurate behaviour
in a*-direction. At T=72 K PT is established to be of the fist
order..
The studies are suppoted by Swiss National
Science Foundation. Grant: N 7SUPJO48718 and partial support
of Russian Fund for Fundumental Resurch N 970218024
1. Kun S.V. Lazarev V.B. et all Isvestiya
Akademii Nauk SSSR, Neorganicheskie Materialy IVNMA 29
(1993) 410-413.
2. Aleksandrova et all. FTT.1997, T39,N5,946-948.