NEW EVIDENCE FOR THE HEXAGONAL MODULATED HIGH TEMPERATURE PHASE IN K2MoxW1-xO4
B.Bzowski1, H. Duda1, J. Kusz1, J. Warczewski1 , M. Behruzi2 & Th. Hahn2
1University of Silesia, Institute of
Physics, ul. Uniwersytecka 4, PL-40007 Katowice, Poland
2Rheinisch - Westflische Technische
Hochschule Aachen, Institut fr Kristallographie, Jgerstrae 17-19,
D-52066 Aachen, Germany, e-mail: warcz@us.edu.pl
Keywords: modulated structures, high-temperature phase,
modulation parameter, K2MoxW1-xO4
There exists an inconsistency in the literature regarding the
modulated phases of the compounds K2MoxW1-xO4
: [1 and 2] state that the modulation occurs in the hexagonal
high-temperature phase, whereas in [3] an orthorhombic
cell for the average crystal structure of twinned K2MoO4
is proposed. In the present paper we have used high-temperature
powder data (Siemens D500) to distinguish between both results.
All reflections of the powder patterns can be indexed in the
frame of a hexagonal modulated phase. The following formula [2]
has been used to define the modulation parameter.
R = H(hkl) +
p*mod(rs) = ha* + kb*
+ lc* + p(ra* + sb*)
,
where : a*, b*, c*, are the reciprocal lattice basis vectors, hkl are the indices, p*mod(rs) is the modulation vector, p = |p*mod|/|a*| and is called a modulation parameter, (r,s) = +-(1,0), (1,-1), (0,1) is the order of the satellite reflection; (r,s) = (0,0) for a main reflection.
Satellite reflections for K2MoO4 at 460oC;
a = 6.3277(4) A, c = 7.9675(4) A, p = 0.298(4)
| h | k | l | r | s | dexp | dcalc |
| 1 1 1 1 1 2 2 2 |
0 0 0 0 0 0 0 0 |
1 2 2 2 2 2 2 2 |
-1 -1 -1 0 1 -1 0 1 |
0 0 1 1 0 1 1 0 |
5,587 3,552 3,349 3,031 2,902 2,361 2,137 2,048 |
5,580 3,550 3,339 3,044 2,917 2,388 2,149 2,053 |
The above results are in agreement with [1,2] and contradict
the results of [3].