Ferroelectric oxide thin-film capacitors find applications in microelectronic systems, mobile platforms, and miniaturized power devices. They can withstand higher electric fields and display significantly larger energy densities than their bulk counterparts and exhibit higher maximum operating temperatures and better thermal stabilities than polymer-based dielectric capacitors. However, ferroelectric oxide thin films typically possess large remanent polarization and exhibit significant dielectric loss, thereby limiting their dischargeable energy densities. Here we demonstrate, using phase-field simulations, that strain can be utilized to modify the polarization response to electric field and thus optimize the energy-storage performance of ferroelectric thin-film capacitors. For example, an in-plane tensile strain can significantly narrow hysteresis loops by reducing the remanent polarization without significantly decreasing the out-of-plane saturated polarization. As a result, both the dischargeable energy density and charge-discharge efficiency can be significantly enhanced. We analysed the domain structures and energy surfaces to understand the underlying mechanisms for the enhancements. We also propose a bending strategy to further improve the dischargeable energy density, which can be achieved, e.g., by growing ferroelectric thin films on a flexible substrate (e.g., mica). This work provides a general strategy to optimize the energy-storage performance of ferroelectric thin-film capacitors for high-energy/power-density storage applications.

铁电氧化物薄膜电容器可用于微电子系统，移动平台和小型化功率器件中。与基于聚合物的介电电容器相比，它们可以承受更高的电场并显示出比其同类产品更大的能量密度，并具有更高的最高工作温度和更好的热稳定性。但是，铁电氧化物薄膜通常具有较大的剩余极化并表现出显着的介电损耗，从而限制了其可放电的能量密度。在这里，我们使用相场仿真证明，可以利用应变来修改对电场的极化响应，从而优化铁电薄膜电容器的能量存储性能。例如，平面内拉伸应变可通过减少剩余极化而显着缩小磁滞回线，而不会显着降低平面外饱和极化。结果，可放电能量密度和充放电效率均可以显着提高。我们分析了域结构和能量表面，以了解增强的潜在机制。我们还提出了一种弯曲策略，以进一步改善可释放的能量密度，这可以通过例如在柔性基板（例如云母）上生长铁电薄膜来实现。这项工作为优化用于高能量/功率密度存储应用的铁电薄膜电容器的能量存储性能提供了一种通用策略。