Band states and shallow hole traps in Pb(Zr,Ti)O3 ferroelectrics

Band structure calculations and electron paramagnetic resonance measurements are used to show that Pb states determine many of the electronic properties of Pb(Zr,Ti)O3 ferroelectric materials. The valence-band edge consists of hybridized Pb s and O p states at all compositions. The conduction-band minimum changes from a Ti d-like Γ25′ state to a Pb p-like X1 state with increasing Zr content. The Pb p character accounts for the relatively small 0.2 eV increase in band gap in the Pb(Ti,Zr)O3 alloys with Zr content compared to the large 2 eV increase in band gap in Ba(Ti,Zr)O3 alloys. The paramagnetic Pb3+ hole center is found to become deeper and acquire some p character as the Zr content is raised. This is attributed to the change in conduction-band character combined with a local off-center displacement of the Pb3+ ion.