Choi, K.J., Biegalski, M., Li, Y.L., Sharan, A., Schubert, J., Uecker, R., Reiche, P., Chen, Y.B., Pan, X.Q., Gopalan, V., Chen, L.Q., Schlom, D.G. and Eom, C.B. (2004) Enhancement of Ferroelectricity in Strained BaTiO3 Thin Films. Science, 306, 1005-1009.