Nonstoichiometry in apatite-type neodymium silicate single crystals

Apatite-type neodymium silicate single crystals were grown by the floating zone method and their electrical conductivity was measured. At a growth rat e of 5 mm/h, the initial part of a crystal grown from a stoichiometric (Nd: Si = 9.33:6) feed rod was inclusion free, but bubble inclusions were observ ed as crystal growth proceeded. An entirely inclusion-free crystal was grow n, even at 5 mm/h, from a feed rod having a composition of Nd:Si = 9.20:6. Inclusions were again formed in the end part of a crystal grown from a feed rod of Nd:Si = 9.05:6. Electrical conductivity of the Nd9.20 crystal was a lmost constant over the whole length, whereas a decrease in the conductivit y was observed along the growth direction for the Nd9.33 crystal. From thes e results, the stoichiometric composition of neodymium silicate is expected to be different from the congruent one, which may exist around Nd:Si = 9.2 0:6. (C) 2000 Elsevier Science B.V. All rights reserved.