Use of ferroelectric hysteresis parameters for evaluation of niobium effects in lead zirconate titanate thin films
The effects of niobium doping on the hysteresis parameters of sol-gel Pb-1.1-x/2(Zr0.53Ti0.47)(1-x)NbxO3 (0 < x < 0.05) have been reported fbr two sets of films with analogous grain size and degree of (111) texture but with different surface microstructures. For both sets, a strong continuous decay of the remnant and maximum polarizations and slope of the hysteresis loop at the coercive field was observed with increasing niobium concentration. The held dependence of the remnant polarization for any given niobium-doped him was identical to the functional field dependence of the undoped reference him, if multiplied by a niobium-concentration-dependent constant. Although the maximum and remnant polarizations decayed as the dopant level increased, their difference remained the same value as that of the undoped him at any given field. The width of the loop (at zero polarization) was insensitive to the niobium concentration at any given held, A linear increase in coercive held asymmetry (up to 40 kV/cm) was observed with niobium addition, yet was field independent and, thus, electrostatic in origin. Niobium governed switching through a reduction of the number of switching domains, without changing the total lattice polarization response. Microstructure-related effects on switching, such as decreased volume fraction of ferroelectric material or field-screening effects due to the presence of a pyrochlore second phase, were eliminated as the origin of the hysteresis changes. This paper has demonstrated how hysteresis features and their field dependencies can be used to separate the effects of niobium-induced microstructural changes from niobium lattice doping influences on the hysteresis loops.