Effects of copper coating on the crystalline structure of fine barium titanate particles

We have investigated the effect of a metal coating-copper-on the tetragonal structure of fine barium titanate (BaTiO3) particles. The BaTiO3 particles were synthesized by a sol-gel method and heat treated at temperatures >900 degrees C for various amounts of time before coating, The copper coating was achieved by an electroless coating technique. The transmission electron microscopy micrographs revealed that the coated powder contained fine BaTiO3 particles that were embedded in copper patches, The X-ray diffractometry patterns showed that the copper coating increased the c/a ratio of the fine BaTiO3 particles. For powders that were heat treated at 900 degrees C for 10 h and were initially cubic, the copper coating changed the c/a ratio, from 1 to 1.0034. For powders that were calcined at 900 degrees C for 20 h and were initially tetragonal, the copper coating further enhanced the c/a ratio, from 1.0028 to 1.0043, When the copper-coated BaTiO3 particles were oxidized, the c/a ratio was reduced to a value that was approximately equal to or below that of the uncoated powders. A conductive coating can eliminate the depolarization energy of an insulating polar particle. The fact that the copper coating promoted the polar tetragonal phase but the nonconductive copper-oxide coating did not was consistent with the interpretation that the presence of the cubic phase (nonpolar) in small BaTiO3 particles was caused by the depolarization effect.