Two new lines of langasite family compositions

Isomorphism of ions in Ca₃Ga₂Ge₄O ₁₄-type structure is considered and criteria of search for new compositions in four-component oxide systems are formulated. The preparation of two new groups of disordered four-component compositions is reported. Ln₃Ga₃Ge₂BeO₁₄, possessing wide range of homogeneity, exist with Ln = La-Eu. Substitution for Be²⁺ in 2d tetrahedral site shifts Ln:Ga ratio from garnet one 3:5 to 1:1 and decreases garnet structure stability. This enables to introduce smaller, then Nd³⁺, rare earth ions Sm³⁺ and Eu³⁺. Four-component solid solutions are found in binary section A₃B_xM₂ Si_4-xO₁₄ of silicate systems AO-BO₂ -M₂O₃-SiO₂ (A=Ca, Sr, Ba; B=Ge, Ti, Sn, Zr; M=Ga, Fe). Some Ti-Ga-silicate compositions look promising for melt crystal growth. Principles of crystallization in four-component system are discussed