Microstructure and dielectric parameters of epitaxial SrRuO3/BaTiO3/SrRuO3heterostructures

Epitaxial films of ferroelectric barium titanate are desirable in a number of applications but their properties are inferior to those of bulk material . Relations between microstructure and dielectric properties may give bette r understanding of limitations. Trilayer heterostructures SrRuO3/BaTiO3/SrR uO3 were grown by laser ablation on (100)LaAlO3 and (100)MgO substrates. Th e BaTiO3 layer was granular in structure. When grown on (100)SrRuO3/(100)La AlO3, it was preferentially a-axis oriented due to tensile mechanical stres s. Using (100)MgO as a substrate, on the other hand, produced a mixture of about equal value of a-axis and c-axis oriented grains of BaTiO3. The diele ctric permittivity, epsilon, of the BaTiO3 layer was almost twice as large, at T > 200 K and f=100 kHz, for the LaAlO3 substrate as compared to the Mg O one. Its maximum value (epsilon/epsilon (0)approximate to 6200) depended on temperature of growth, grain size, and electric field and compares well with optimal values commonly used for ceramic material. The maximum in the epsilon (T) shifted from about 370 to 320 K when the grain size in the BaTi O3 film decreased from 100 to 40 nm. At T < 300 K, hysteresis loops in pola rization versus electric field were roughly symmetric. The BaTiO3 films gro wn on (100)SrRuO3/(100)MgO exhibit the largest remnant polarizations and co ercive fields in the temperature range 100-380 K. (C) 2001 American Institu te of Physics.