The dependence of the structural parameters on compositional deviation
s of CuGaSe2 has been studied. These deviations have been induced alon
g an ingot by a single fusion of the components at 1150 degrees C and
subsequent slow cooling in a stationary ampoule in a vertical furnace.
All along the sample a single chalcopyrite phase is present and a com
positional gradient along the ingot was found by energy-dispersive ana
lysis of X-rays (EDAX) measurements, the upper part being rich in Ga (
series B) and the lower part in Cu (series A), with Cu/Ga ratios of 0.
95 and 1.1 respectively. A hypothesis of the existence of two phases i
n the melt is proposed to explain these facts. The unit cell parameter
s, anion displacement and Cu and Ga occupation numbers in their sublat
tices were analysed by X-ray powder diffraction and Rietveld refinemen
t methods. In series A the occupation numbers are near stoichiometry,
while in series B a Cu defect appears. In both series, changes in unit
cell parameter are related to changes in Cu content, suggesting the p
resence of a fraction of Cu ions either as interstitials or at Ga site
s when Cu is in excess, or of Cu vacancies in its sublattice when ther
e is a Cu deficiency. (C) 1998 John Wiley & Sons, Ltd.