Influence of precursor solutions on the ferroelectric properties of sol-gel-derived lanthanum-modified lead titanate (PLT) thin films

Precursor chemistry was found to have a dominant effect on the electrical properties of sol-gel-derived Pb0.85La0.15TiO3 (PLT15) thin films prepared using different precursor sources for lanthanum, namely, lanthanum acetate dissolved in acetic acid (LAA) and lanthanum 2-methoxyethoxide in 2-methoxy-ethanol (LMM). The LMM-derived PLT15 films had lower dielectric constants (K-LMM = 394, K-LAA = 548, measured at 100 kHz, applying 500 mV oscillation voltage), poorer polarization hysteresis characteristics, and higher leakage current densities (J(LMM) similar to 1.5 x 10(-7) A/cm(2), JLAA similar to 2 x 10(-9) A/cm(2), measured at 10 kV/cm field). Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) measurements in conjunction with Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicate that better removal of C-O moieties are the key step to yield improved electrical properties in these films. Possibly, C-O moieties reduce the metallic oxides to their corresponding metals and the presence of the metallic constituent(s) (e.g., lead), in turn deteriorate the electrical properties. In line with these postulations it was found that, when the pyrolysis temperature is increased from 450degrees to 550degreesC, the organic contents of LMM-derived films are reduced and their electrical properties are indeed comparable to that of the LAA-derived films.