Abstract
Dielectric crystals having composition in the vicinity of Ba3.75R9.5Ti18O54 and/or BaR2Ti4O12 (R=La, Nd and Sm) were obtained from the melts with BaR2Ti5O14 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, Pbn21 (No. 33) or Pbnm (No. 62); a=12.267(5), b=22.410(9), c=7.732(6) Å for Ba3.75La9.5Ti18O54; a=12.189(3), b=22.319(6), c=7.677(4) Å for Ba3.75Nd9.5Ti18O54; a=12.142(4), b=22.300(6), c=7.653(4) Å for Ba3.75Sm9.5Ti18O54. Space group of the fundamental lattice is Pba2 (No. 32) or Pbam (No. 55). The dielectric constants, εr, of Ba3.75R9.5Ti18O54 (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 BaR2Ti5O14 composition including secondary phases.
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