GROWTH OF NAGDSIO4 CRYSTALS FROM AN NAF F LUX

Colorless and transparent crystals of NaGdSiO4 were grown from an NaF flux by a slow cooling method. The solubility of NaGdSiO4 in NaF incre ased with increasing temperature. At 1100 degrees C, NaGdSiO4 was diss olved in NaF at a concentration of about 0.87 mol%. The eutectic tempe rature was 990 +/- 5 degrees C. The flux growth was conducted by heati ng mixtures at 1100 degrees C for 10 h, followed by cooling to 600 deg rees C at a rate of 5 degrees C h(-1). The mixture containing 0.25 mol % solute produced only needle crystals. The mixtures containing 0.5 an d 0.75 mol% solute gave needle and prismatic crystals. Needle, prismat ic and bulky crystals were grown from the mixtures containing 1-5 mol% solute. When the mixtures contained more than 6 mol% solute,only bulk y crystals were grown. The maximum sizes of the needle, prismatic and bulky crystals were 3.6 mm x 0.2 mm, 3.2 mm x 0.6 mm and 2.3 mm x 1.2 mm, respectively. The most suitable solute content was 0.75 mol% for t he growth of needle crystals. In the case of the growth of prismatic a nd bulky crystals, the most suitable solute content was 1 mol%. The gr own crystals belonged to the tetragonal system and the lattice paramet ers observed were a = 11.743 +/- 0.001 Angstrom and c = 5.443 +/- 0.00 1 Angstrom. The basic form of grown crystals was an eight-sided prism with pyramidal end faces. The indices of all the faces were {100}, {11 0} and {121}. The EPMA data showed that sodium, gadolinium, silicon an d oxygen were distributed almost homogeniously in the crystals. The de nsity was 4.82 +/- 0.02 g cm(-3).