V 5 + ionic displacement induced ferroelectric behavior in V-doped ZnO films

V-doped ZnO films have been prepared on Si(111) substrates by direct current reactive magnetron cosputtering. Hysteresis loops of polarization–applied field characteristics with a remnant polarization of 0.2μC∕cm2 were obtained in (2.5at.%) V-doped ZnO films, indicating the ferroelectric behavior exists in this system. This is demonstrated by displacement-voltage curves, which show typical butterfly shapes. X-ray absorption near-edge structure (XANES) spectrum at V K edge shows that V is in the 5+ state replacing Zn. Furthermore, the calculations of the XANES spectra indicate that a V5+ ionic displacement of 0.15Å is responsible for the ferroelectric behavior.