Background oxygen effects on pulsed laser deposited Na0.5K0.5NbO3 films: From superparaelectric state to ferroelectricity

Ambient oxygen pressure in a pulsed laser deposition process has been obser ved to have a critical influence on the compositional, crystalline, and ele ctrical properties of Na0.5K0.5NbO3 (NKN) thin films grown onto polycrystal line Pt80Ir20 and SiO2 (native oxide)/Si(111) substrates. Films prepared at high oxygen pressure (similar to 400 mTorr) were found to be single phase and highly c-axis oriented. X-ray diffraction theta-2 theta scans and rocki ng curve data show a strong effect of NKN film self-assembling along the [0 01] direction regardless of the substrate texture. The high dielectric perm ittivity of 550, low dissipation factor of less than 3%, and high remanent polarization of 12 mu C/cm(2) indicate the high ferroelectric quality of th e fabricated film. The role of the high-energy component of the erosion pro ducts has been proven to be crucial to film performance. On the other hand, films grown at low oxygen pressure (similar to 10 mTorr) have been found t o be mixed phases of ferroelectric NKN and paraelectric potassium niobates. These films have shown superparaelectric behavior: 5% tunability at an ele ctric field of 100 kV/cm, losses as low as 0.3%, and excellent stability to temperature and frequency changes. (C) 2000 American Institute of Physics. [S0021-8979(00)08709-0].