Expansion of the Chemistry of Nitridometallates of 3d Transition Metals through a Novel High-Pressure Synthesis Approach

本博士后项目将为迄今为止探索较少的3d过渡金属氮杂环化合物开辟一条新的合成途径。这些组成为A-M-N的化合物，其中A是正电性金属，M是3d过渡金属，由于它们在自旋电子学、热电学、超导体和能量转换材料中作为半金属的潜在应用，在90年代已经被研究。然而，近年来，他们的探索几乎停滞不前，部分原因可能是这些材料的合成困难。障碍是惰性或温度不稳定的起始材料，最重要的是氮化物的强烈竞争性氧化还原分解。在环境压力下，由于这种分解，只有一个很小的温度窗口可以进行反应。在这个项目中，3d金属的金属氮化物化学将通过一种创新的高压方法复活。通过施加吉帕斯卡范围内的压力，氧化还原分解遵循勒夏特列原理被抑制，并且温度窗口被扩大。因此，通过密闭加压的反应空间，可以实现在常压下无法实现的新的合成策略。首先，通过改变压力、温度以及不同的反应类型和起始原料，如叠氮化物、酰胺、氮化物和复分解反应，建立新的合成路线。由于3d金属的物理性质，选择氮钛酸盐和铁酸盐作为起始体系。探索氮氧化物的主要问题是合成现有结构家族的缺失成员，例如MFeN 2化合物（M = Ca，Sr）的Ba 2FeN 2，以及合成具有有趣特性的预测材料，如热电BaTiN 2。长期目标，这可以从这个项目中发展，包括在这些系统中的金属-绝缘体转变的调查，以及高压和高温对阴离子结构的影响的研究，因为几个已知的nitrididazolates功能结构基序从主族化学。在该项目的第二部分中，将研究所获得化合物的物理性质，如磁性，电阻率和热容，例如温度和施加的磁场。由于对这些性质知之甚少，一个目标是丰富对氮杂环丁烷酸盐的结构-性质关系的理解。我们有信心，这个博士后项目可以导致迷人的见解的结构化学以及3d过渡金属的nitridditrilates的物理性质。

In this postdoctoral project a new synthesis pathway shall be opened for the hitherto little explored nitridometallates of the 3d transition metals. These compounds of composition A–M–N, in which A is an electropositive metal and M a 3d transition metal, had been investigated in the 90s owing to their potential application as semimetals in spintronics, thermoelectrics, superconductors, and energy conversion materials. Their exploration, however, almost came to a standstill in recent years, which might in part be owed to the difficult synthesis of these materials. Obstacles are inert or temperature labile starting materials and most important the strongly rivalling redox decomposition of the nitrides. At ambient pressures there is only a small temperature window available to conduct reactions due to this decomposition.The nitridometallate chemistry of the 3d metals will be revived with an innovative high-pressure approach in this project. By applying pressures in the gigapascal range the redox decomposition is suppressed following the principle of Le Chatelier and the temperature window is enlarged. Hence, through the enclosed and pressurized reaction space, new synthesis strategies can be realized that are inapplicable at ambient pressures.Firstly, new synthesis routes shall be established through variation of pressure, temperature, as well as different reaction types and starting materials like azides, amides, nitrides and metathesis reactions. Nitridotitanates and -ferrates are chosen as starting systems owing to the physical properties of the 3d metals. Leading questions for the exploration of the nitridometallates are the synthesis of missing members of existing structural families for example Ba2FeN2 of the MFeN2 compounds (M = Ca, Sr), and the synthesis of predicted materials with intriguing properties like the thermoelectric BaTiN2. Long-term goals, which can evolve from this project, include the investigation of the metal-insulator transition in these systems as well as the study of the influence of high pressures and temperatures on the anion structures, since several known nitridometallates feature structural motifs from main group chemistry. In the second part of this project, physical properties like magnetism, resistivity, and heat capacity of obtained compounds will be investigated in dependency on for example temperature and applied magnetic field. As only little is known about such properties, one goal is to enrich the understanding of the structure-property relations of nitridometallates. We are confident that this postdoctoral project can lead to fascinating insights into the structural chemistry as well as the physical properties of the nitridometallates of the 3d transition metals.