Field-induced ferroelectricity and tunable response in paraelectric PbxSr1−xTiO3 epitaxial films

Abstract

The widespread use of ferroelectric materials in tunable electronic devices is often limited by energy dissipation at domain walls in the ferroelectric state. Low dielectric losses and high tunability can be achieved by operating the material in the paraelectric phase under an external electric field. Under these conditions, a domain-free, field-stabilized ferroelectric-like state can be induced, particularly near phase boundaries or multicritical points. We investigate the electric-field control of dielectric and piezoelectric properties in paraelectric PbxSr1−xTiO3 (PST) thin films epitaxially constrained on cubic substrates. Using a Landau–Ginzburg–Devonshire thermodynamic potential that incorporates both polarization and octahedral tilting as coupled order parameters, we construct the room-temperature (300 K) phase diagram in the misfit strain–composition (um–x) plane. Within the paraelectric region, we analyze the system’s responseunder a perpendicular electric field (Ez = 100 kV cm−1), which induces a uniaxial, domain-free ferroelectric-like state, often referred to as a ‘forced’ ferroelectric. We calculate the field-dependent permittivities ( ε33, ε11) and induced piezoelectric coefficients ( dij, eij) along a path within the paraelectric phase near the adjacent ferroelectric phase boundaries. Our results show a pronounced enhancement of dielectric tunability t(ε) and non-zero piezoelectric response in regions near the multicritical point (um ≈ 0, x ≈ 0.138), where the paraelectric phase borders the c-phase (tetragonal, P4mm), r-phase (rhombohedral-like monoclinic, Cm), and aa-phase (orthorhombic, Amm2). The most pronounced effects occur near the boundary with the c-phase, where the out-of-plane polarization mode undergoes softening. These findings indicate that operating PST thin films in the paraelectric phase under an external bias enables low-loss, highly tunable behavior, making them promising candidates for reconfigurable microwave and electronic devices.