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 rate 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 observed as crystal growth proceeded. An entirely inclusion-free crystal was grown, 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 almost constant over the whole length, whereas a decrease in the conductivity was observed along the growth direction for the Nd9.33 crystal. From these results, the stoichiometric composition of neodymium silicate is expected to be different from the congruent one, which may exist around Nd:Si = 9.20:6. (C) 2000 Elsevier Science B.V. All rights reserved.