New Multifunctional Transition Metal Oxides with Correlated Electronic Properties

在材料研究部固态和材料化学项目的支持下，本研究的重点是具有低维，强相互作用电子性质的新型过渡金属氧化物的合成和表征，以发现具有基本重要和技术上有用行为的新型多功能极性和磁性电子材料。该计划的重点是结构和物理性质的详细表征，以了解结构-性质的关系。事实一再证明，这种类型的基础研究为发现新材料提供了基础，从而导致新的现象和有用的应用。这项工作将影响PI实验室博士后、研究生和本科生在新型功能固态材料的实验合成和表征方面的培训和教育。PI与国内外其他科学家和凝聚态理论家的合作工作为学生的科学培训和教育提供了额外的更广泛的影响。这些研究不仅有望为控制新型电子和磁性材料的特性提供关键见解，而且还将为发现的材料在微电子和磁电子学中的潜在应用提供更广泛的影响，用于计算机，传感器和通信。这些都是保持美国全球技术领先地位的关键领域。技术摘要：本实验计划的重点是合成和表征具有强相关电子性质的新型功能过渡金属化合物，这些化合物处于电子和结构不稳定的边缘，并通过不稳定区域以可控的方式微调竞争电子相互作用。经验表明，当晶格、自旋、电荷、轨道和其他电子相互作用相互竞争时，可能会发现具有新行为的材料。这种相互竞争的相互作用可以导致有趣和有用的性质，包括金属到绝缘体的转变、磁有序、自旋和电荷密度波的不稳定性、多铁性、磁电行为和超导性。在低维材料中，竞争相互作用的相互作用增强了。感兴趣的体系包括：(1)过渡金属Ruddlesden-Popper （RP）层状相AO(ABO)n；(2)双层钙钛矿AA'BB'O6；(3)四重钙钛矿AA'3B4O12；(4) AA' bb ' O6新非中心对称刚玉相。这些复杂的、强相关的电子材料有一个共同的特点，即局部自由度和流动自由度之间的相互作用，一个高度可变的传导电子带宽，可以通过改变晶体结构、化学成分、外部应变和无序程度等来调节。带宽的可变性导致了各种重要的现象，包括由温度、磁场、光照、压力、晶格畸变和其他变量的变化驱动的金属-绝缘体转变（或急剧交叉）。我们预计，在这些跃迁附近，输运、电子和磁性也会发生巨大变化，并且是可调的。这项工作是系统地研究独特的合成路线，包括固态，高压，“化学灌洗”水热，以稳定新的和有趣的过渡金属化合物。有希望的新相的晶体生长（对研究各向异性至关重要）将通过通量生长、化学蒸气输送和电解等方法进行尝试。将进行一系列物理测量，包括x射线和中子衍射，电子衍射和透射电子显微镜，温度相关输运，比热，介电和磁性测量。

Non-Technical AbstractWith support from the Solid State and Materials Chemistry program in the Division of Materials Research, the focus of this research is the synthesis and characterization of new transition metal oxides with low-dimensional, strongly interacting electronic properties to discover new multifunctional polar and magnetic electronic materials with fundamentally important and technologically useful behavior. The emphasis of the program is the detailed characterization of the structure and physical properties to understand the structure-property relationships. It has been demonstrated repeatedly that fundamental research of this type provides the basis for discovering new materials, which lead to novel phenomena and useful applications. The proposed work will impact the training and education of Postdoctoral fellows, graduate and undergraduate students in the PI's laboratory in the experimental synthesis and characterization of new functional solid state materials. Collaborative work of the PI with other scientists and condensed matter theorists nationally and internationally provides additional broader impact for the scientific training and education of students. These studies are expected to yield not only critical insight for the control of the properties of novel electronic and magnetic materials, but also to provide broader impacts for potential applications of the discovered materials in microelectronics and magneto-electronics for computers, sensors and communications. These are critical areas for maintaining US technological leadership worldwide. Technical AbstractThe focus of the experimental program is the synthesis and characterization of new functional transition metal compounds with strongly correlated electronic properties that are on the verge of electronic and structural instabilities, and to fine-tune the competing electronic interactions through the unstable region in a controlled way. Experience shows that materials with novel behavior are likely to be discovered, when lattice, spin, charge, orbital and other electronic interactions compete. Such competing interactions can lead to interesting and useful properties, including metal-to-insulator transition, magnetic ordering, spin and charge density wave instabilities, multiferroic, magnetoelectric behavior and superconductivity. In low-dimensional materials the interplay of competing interactions is enhanced. Systems of interest include: (1) Transition metal Ruddlesden-Popper (RP) layered phases, AO(ABO)n; (2) Layered double perovskites, AA'BB'O6; (3) Quadruple perovskites AA'3B4O12; (4) AA'BB' O6 new non-centrosymmetric corundum phases. These complex, strongly correlated electronic materials share the common feature of an interplay between localized and itinerant degrees of freedom, a highly variable conduction electron band-width, which may be tuned by changing e.g., the crystal structure, chemical composition, external strain and degree of disorder. The variability of band-width leads to a variety of important phenomena, including metal-insulator transitions (or sharp crossovers) driven by variation of temperature, magnetic field, illumination, pressure, lattice distortion and other variables. We expect that in the vicinity of these transitions the transport, electronic and magnetic properties will also change dramatically and will be tunable. The effort is a systematic study of unique synthetic routes including solid state, high pressure, "chemo douche" hydrothermal for the stabilization of new and interesting transition metal compounds. Crystal growth (essential to study anisotropic properties) of promising new phases will be attempted by e.g., flux growth, chemical vapor transport, and electrolysis. The characterization of properties by a battery of physical measurements including x-ray and neutron diffraction, electron diffraction and transmission electron microscopy, temperature dependent transport, specific heat, dielectric and magnetic properties measurements will be carried out.