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尚未被探索的三维过渡金属金属氮化金属化合物开辟一条新的合成途径。这些由A - M - n组成的化合物，其中A是正电金属，M是三维过渡金属，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年代已经被研究过。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，最重要的是强烈对抗氮化物的氧化还原分解。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。在该项目中，3d金属的氮化金属化学将通过创新的高压方法得到恢复。通过在千兆帕斯卡范围内施加压力，氧化还原分解遵循勒夏特列原理被抑制，温度窗被扩大。因此，通过封闭和加压的反应空间，可以实现在环境压力下不适用的新的合成策略。首先，通过压力、温度的变化，以及叠氮化物、酰胺、氮化物、复分解反应等不同的反应类型和原料，建立新的合成路线。由于三维金属的物理性质，选择硝酸钛酸盐和高铁酸盐作为起始体系。探索金属氮化盐的主要问题是合成现有结构家族的缺失成员，例如MFeN2化合物（M = Ca, Sr）中的Ba2FeN2，以及合成具有有趣性质的预测材料，如热电BaTiN2。长期目标，可以从这个项目中发展，包括研究这些系统中的金属-绝缘体转变，以及研究高压和高温对阴离子结构的影响，因为一些已知的氮化金属具有主基团化学的结构基序。在该项目的第二部分，将研究所获得化合物的物理性质，如磁性、电阻率和热容量，这些性质取决于温度和外加磁场。由于对这种性质的了解很少，一个目标是丰富对氮化金属的结构-性质关系的理解。我们相信，这个博士后项目可以导致对三维过渡金属氮化金属的结构化学和物理性质的迷人见解。

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.