Structural study of monoclinic KGd(WO4)(2) and effects of lanthanide substitution

The crystal structure of monoclinic KGd(WO4)(2) (KGW) has been refined at r oom temperature by using single-crystal X-ray diffraction data. The unit-ce ll parameters are a = 10.652 (4), b = 10.374 (6), c = 7.582 (2) Angstrom, b eta = 130.80 (2)degrees, with Z = 4, in space group C2/c. The linear therma l expansion tensor has been determined and the principal axes are [302], [0 10] and [106]. The principal axis with maximum thermal expansion (alpha (33 )' = 23.44 x 10(-6) K-1), X-3', was located 12 degrees from the c axis. Und oped crystals of KGW and crystals that were partially doped by Pr, Nd, Ho, Er, Tm and Yb were grown by the top-seeding-solution growth slow-cooling me thod. The effect of doping on the KGW structure was observed in the cell pa rameters and in morphological changes. The changes in parameters follow the changes in lanthanide ionic radii. The doped crystals show {021} and {(2) over bar 21} faces in addition to the {110}, {(1) over bar 11}, {010}, {130 } and {310} faces which basically follow the habit of the undoped KGW cryst als. The development of the faces is related to the number of the most impo rtant periodic bond chains parallel to them.