The orientation dependences of the converse longitudinal piezoelectric constant d(33,f), and the in-plane converse piezoelectric constant e(31.f), are calculated for tetragonal barium titanate epitaxial films. The calculations demonstrate that both e(31,f) and d(33.f). have their maximum values along an axis close to the (1 1 1) direction of the pseudo-cubic system, which are similar to the orientation dependence results for a tetragonal BaTiO3 single crystal. The calculated piezoelectric constants for a (1 1 1) oriented BaTiO3 epitaxial film (e(31,f) = -23 C/m(2), d(33,f) = 124 pm/V) suggest that it is a good candidate material for lead-free MEMS applications. (c) 2005 Elsevier B.V. All rights reserved.