Origin of bias-voltage-dependent transient negative capacitance in PZT ferroelectric capacitor with labyrinthine-like domains
We investigated how the bias-voltage-dependent variation in the ferroelectric domain switching pathways affects the transient negative capacitance in multidomain PZT ferroelectric capacitor with labyrinthine-like domains having, primarily, 90$^\circ$ walls. Using the vector piezoresponse force microscopy, x-ray photoelectron spectroscopy, and energy dispersive x-ray spectroscopy, we show that, together with strain, local variation in composition results in the formation of labyrinthine domains in epitaxial films of thickness $\sim$1 $μ$m. Clear signature of emergence of bias-voltage-dependent pathways could be observed in the Raman modes exhibiting splitting due to an intermediate state - different from the initial and final states - at the ``intermediate state of switching". The polarization relaxation patterns also show different states emerging depending on the bias voltage characteristics. The phase-field simulation of relaxation of ``intermediate state of switching" corroborates the experimental results and also exhibits dependence of the domain-wall area on the bias voltage and damping parameter. Combining the results of experiments and theoretical calculation, we show, therefore, that the variation of bias voltage leads to a change in the domain switching pathways and each pathway is associated with specific domain-wall area at the ``intermediate state of switching". Since, the net domain-wall area at the ``intermediate state of switching" governs the magnitude of transient negative capacitance, this work thus traces the origin of tunability of transient negative capacitance in PZT ferroelectric capacitor.