The electrocaloric effect represents an adiabatic temperature change or isothermal entropy change upon the application or removal of an external electric field. However, the effect of the repetitive bipolar/unipolar electric field on the electrocaloric effect in ferroelectrics is not well understood. In this work, the electrocaloric effect after both bipolar and unipolar electrical cycling in Pb0.92La0.08Zr0.65Ti0.35O3 relaxor thin films has been indirectly evaluated using the Maxwell relationship. It was found that at room temperature, the electrocaloric temperature change ΔT under higher electric fields decreases gradually from a positive value to a negative one with the increase in the bipolar/unipolar fatigue cycle number. Intriguingly, around the Curie temperature, the positive ΔT of the film after bipolar/unipolar cycling was found to decrease under low or intermediate electric fields, while it remains almost unchanged under high electric fields. This behavior is attributed to the pinning effect of defects caused by phase decomposition during both bipolar and unipolar fatigue. Note that the increase in polarization by temperature induced domain depinning close to room temperature after the fatigue process is manifested by using the Maxwell relation indirectly. Our work further reveals the origin of both the electrocaloric effect and ferroelectric electrical fatigue and is important for the applications of practical electrocaloric refrigerators.

中文翻译：

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极化疲劳对弛豫Pb0.92La0.08Zr0.65Ti0.35O3薄膜电热效应的影响

电热效应代表在施加或去除外部电场时的绝热温度变化或等温熵变化。然而，重复的双极/单极电场对铁电体中电热效应的影响尚不清楚。在这项工作中，使用麦克斯韦关系间接评估了 Pb0.92La0.08Zr0.65Ti0.35O3 弛豫薄膜中双极和单极电循环后的电热效应。发现在室温下，随着双极/单极疲劳循环次数的增加，较高电场下的电热温度变化ΔT从正值逐渐减小到负值。有趣的是，在居里温度附近，发现双极/单极循环后薄膜的正 ΔT 在低或中电场下降低，而在高电场下几乎保持不变。这种行为归因于双极和单极疲劳期间由相分解引起的缺陷的钉扎效应。请注意，通过间接使用麦克斯韦关系，可以看出疲劳过程后温度引起的域脱离接近室温而导致的极化增加。我们的工作进一步揭示了电热效应和铁电电疲劳的起源，对实际电热冰箱的应用具有重要意义。这种行为归因于双极和单极疲劳期间由相分解引起的缺陷的钉扎效应。请注意，通过间接使用麦克斯韦关系，可以看出疲劳过程后温度引起的域脱离接近室温而导致的极化增加。我们的工作进一步揭示了电热效应和铁电电疲劳的起源，对实际电热冰箱的应用具有重要意义。这种行为归因于双极和单极疲劳期间由相分解引起的缺陷的钉扎效应。请注意，通过间接使用麦克斯韦关系，可以看出疲劳过程后温度引起的域脱离接近室温而导致的极化增加。我们的工作进一步揭示了电热效应和铁电电疲劳的起源，对实际电热冰箱的应用具有重要意义。