On the origin of oxygen isotope exchange induced ferroelectricity in strontium titanate Hai-Yao Deng, Chi-Hang Lam and H.T. Huang Eur. Phys. J. B, 85 7 (2012) 234 Published online: 03 July 2012 DOI: 10.1140/epjb/e2012-30069-3