The phase diagram of the La 2 O 3 —Ga 2 O 3 —SiO 2 system around La 3 Ga 5 SiO 14 was investigated by a different thermal analysis and the quenching method. On the basis of this diagram, single crystals of La 3 Ga 5 SiO 14 were grown from different starting melt compositions by the Czochralski technique. The effect of starting melt composition on crystal quality was examined by measuring the variation of chemical composition and lattice parameters along the growth axis. The congruency and the existence of a solid solution range of La 3 Ga 5 SiO 14 are discussed. ( 1999 Elsevier Science B.V. All rights reserved. PACS: 81.10.Fq; 81.30.T; 74.62.Bf