Superlattice and Dielectric Properties of BaO-R₂O₃-TiO₂ (R=La, Nd and Sm) Microwave Dielectric Compounds

Abstract

Dielectric crystals having composition in the vicinity of Ba 3.75 R 9.5 Ti 18 O 54 and/or Ba R 2 Ti 4 O 12 ( R =La, Nd and Sm) were obtained from the melts with Ba R 2 Ti 5 O 14 composition. A superlattice with two times the fundamental lattice spacing along the c -axis has been found in the three kinds of crystals. Crystal data of the superlattice are as follows: orthorhombic, P b n 2 1 (No. 33) or P b n m (No. 62); a =12.267(5), b =22.410(9), c =7.732(6) Å for Ba 3.75 La 9.5 Ti 18 O 54 ; a =12.189(3), b =22.319(6), c =7.677(4) Å for Ba 3.75 Nd 9.5 Ti 18 O 54 ; a =12.142(4), b =22.300(6), c =7.653(4) Å for Ba 3.75 Sm 9.5 Ti 18 O 54 . Space group of the fundamental lattice is P b a 2 (No. 32) or P b a m (No. 55). The dielectric constants, ε r , of Ba 3.75 R 9.5 Ti 18 O 54 ( R =Nd and Sm) are in the high range from 78 to 86, and unloaded Q values are in the range of 2400 to 3000. The excellent values of single phase are better than those of Ba R 2 Ti 5 O 14 composition including secondary phases.