Research of the Free-Carrier-Induced Ferroelectric Metal in Layered Perovskite Oxides

铁电金属结合了铁电性和金属性，这两种看似相互排斥的性质在一个系统中，强烈地激起了研究界的兴趣。铁电体具有自发和可逆的电极化，有着广泛的应用前景，并提出了一些基本问题。一般来说，它们是绝缘体。巡游载流子的引入有望屏蔽长程库仑力并淬灭铁电性。当安德森和布朗特从理论上提出类铁电金属的存在，并在实验上观察到LiOsO 3中存在类铁电结构转变时，这一传统观念被打破。虽然铁电/极性金属的一些理论预测已经报道，实验观察仍然是相当罕见的。本项目的核心课题是扩大该材料家族的成员，研究铁电/极性金属材料的非常规特性。我们在2022财年（FY 2022）取得了两项成果。首先，成功地合成了一种新的金属过渡金属氧化物（与LiOsO 3相同）的多晶形式，其在低温下具有铁电性结构转变。其次，制备了一系列具有Ruddlesden-Popper型结构的载流子掺杂层状钙钛矿氧化物。

Ferroelectric metals combining ferroelectricity and metallicity, two seemingly mutually exclusive properties in one system, strongly stirred the research community. Ferroelectrics with a spontaneous and reversible electric polarization, are promising for a wide range of applications and pose a number of fundamental questions. In general, they are insulators. Introducing itinerant charge carriers is expected to screen the long-range coulomb forces and quench ferroelectricity. This conventional concept was broken when the existence of ferroelectric-like metal was theoretically proposed by Anderson and Blount and the ferroelectric-like structural transition in metallic was experimentally observed in LiOsO3. Although several theoretical predictions of ferroelectric/polar metals have been reported, the experimental observations are still rather rare so far. The core issue of this project is to extend the members of this material family and research the unconventional properties of ferroelectric/polar metal materials.We have achieved two things in the fiscal year 2022 (FY2022). First, one new metallic transition metal oxide (same to LiOsO3) with ferroelectric-like structural transition at low temperature was successfully synthesized in polycrystalline form. Second, a series of carrier doped layered perovskite oxides with Ruddlesden-Popper type structure was prepared.