Journal of Crystal Growth 212 (2000) 469}475 Melt growth of (Tb,Lu)  Al  O  mixed garnet "ber crystals Valery I. Chani*, Akira Yoshikawa, Hiroshi Machida, Tsuguo Fukuda Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan Tokin Co., 1-1, Asahi-Cho 7-Chome, Shiroishi, Miyagi 989-0223, Japan Received 24 December 1999; accepted 4 January 2000 Communicated by M. Schieber Abstract The substitution phenomenon in the (Tb,Lu)  Al  O  mixed garnet crystals have been studied by solidi"cation of corresponding stoichiometric melts using micro-pulling-down apparatus. By substitution of Tb with Lu, the tendency of TbAlO  perovskite phase formation in undoped Tb  Al  O  decreases. Although growth of mixed crystals in general does not allow uniform distribution of constituents in the resulting material, the invariant point was found to exist in the system studied in the vicinity of Tb  Lu  Al  O  composition. Thus, the uniform single-crystal "bers of the above materials up to 500 mm in length and about 1.3 mm in diameter were produced at a pulling-down rate of 1.2 mm/min.  2000 Elsevier Science B.V. All rights reserved. PACS: 81.10; 81.05.L; 81.05.Z; 81.10.F; 64.75; 81.30.D; 64.75 Keywords: Terbium}aluminum garnet; Lutetium}aluminum garnet; Substitution; Fiber; Faraday rotator; Micro-pulling-down method; Mixed crystal 1. Introduction Terbium}aluminum garnet, Tb  Al  O  (TAG) is a well-known optical material of technological importance for use as a Faraday e!ect optical iso- lator [1]. Recently, phase diagram of the Tb  O  }Al  O  binary system was reported [2], and it was shown that the TAG compound melts incongruently with a prime crystallization of * Corresponding author. Institute for Materials Research, Fukuda Laboratory, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Tel.: #81-22-215-2103; fax: #81-22-215-2104. E-mail address: chani@lexus.imr.tohoku.ac.jp (V.I. Chani). TbAlO  perovskite (TAP) phase from the melt cor- responding to stoichiometry of TAG. Therefore, growth of TAG crystals by conventional Czoch- ralski technique is almost impossible. According to Ref. [2], use of Al  O  enriched melt with a ratio of Tb  Al  O  : 0.3Al  O  "1.0 : 0.3 results in single- phase garnet formation. Recently, it was observed that the garnet phase in the Tb  O  }Al  O  system can be stabilized by partial substitution of Tb with Yb [3]. Thus, the (Tb,Yb)  Al  O  (TYAG) garnets "bers of good optical quality were grown by the micro-pulling-down (-PD) technique from the Tb  Yb  Al  O  melt (x"0.8}1.0). Attention has been focused [3] on crystal chemistry of both garnet and perovskite structural families, and it was supposed that the substitution with other small 0022-0248/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 0 2 1 - X