Crystal structures, phase transitions and physical properties of new double perovskites as advanced energy materials

本方案旨在研究双钙钛矿化合物及其作为先进能源材料的应用。主要目标是合成新的化合物，测定它们的晶体结构和相应的物理性质，以及它们在低温和高温下的相变行为。这些物质的合成将基于不同的方法，如固相反应法、水热法和共沉淀法，以获得细小的多晶、纳米颗粒或制备单晶。X射线衍射研究表明，双钙钛矿的结构随温度和化学成分的变化而变化。对于这两个变量，这类双钙钛矿材料表现出一系列的结构相变。此外，由于这些效应，双钙钛矿材料呈现出有趣的电子和磁性转变。通式为A2BB‘O6和AA’BB‘O6的双钙钛矿材料表现出许多功能性质，如铁电性、铁磁性、多铁性、巨磁电阻，甚至高温超导性能，这些性质源于A和B位上存在的化学元素的特性，其中A和A’可以是钙或锶，B是磁性的3d过渡金属离子，B‘将是第4和第5排过渡金属离子[1，2]。交流(AC)磁化率测量将被用来研究磁相变和随时间的自旋动力学。我们还将通过使用密度泛函理论方法(DFT方法)(用于声子色散和带隙行为的电子态密度，用于解释红外和拉曼光谱中的模式的声子态密度)来计算晶格参数、带隙和态密度来研究这些物理性质的转变。该项目将有助于了解这些材料的物理性质，还将涵盖这些有趣化合物晶体结构方面缺乏的理论数据，以便将它们用于与能源相关的技术。

The present proposal aims to study double-perovskite compounds and their application as advanced energy materials. The main objectives are the synthesis of new compounds, the determination of their crystal structures and the corresponding physical properties as well as their phase-transition behavior at low and high temperatures. The synthesis of these substances will be based on different methods such as solid-state reaction, hydrothermal and coprecipitation to obtain fine particles of polycrystalline, nanoparticles or to prepare a single crystal. X-ray diffraction studies will indicate the structural evolution according to the temperature and chemical composition of the double perovskite. With respect to these two variables, these classes of double-perovskite materials exhibit a large series of structural phase transitions. In addition, double-perovskite materials present interesting transitions of the electronic and magnetic properties because of those effects. Double-perovskite materials with the general formulas A2BB'O6 and AA'BB'O6 show many functional properties such as ferroelectricity, ferromagnetism, multiferroicity, giant magnetoresistance, and even high-temperature superconductivity, these properties originate from the characteristics of the chemical elements present on sites A and B, where A and A' might be Ca or Sr, B is occupied by magnetic 3d transition metal ions and B' will be 4th and 5th rows transition metal ions [1, 2]. Alternating Current (AC) magnetic susceptibility measurements will be used to study magnetic phase transitions and spin dynamics with time. We will also study these transitions of physical properties by calculating lattice parameters, band gaps, and density of states using Density Functional Theory method (DFT method) (EDOS (Electronic Density Of States) for phonon dispersion and band gaps behavior, PDOS (Phonon Density Of States) for interpretation of modes in IR and Raman spectroscopy). This project will help to understand the physical properties of these materials and it will also cover the lacking theoretical data on crystal structures of these interesting compounds, to use them in energy-related technologies.