Kubitza Niels, Reitz Andreas, Zieschang Anne-Marie, Pazniak Hanna, Albert Barbara, Kalha Curran, Schlueter Christoph, Regoutz Anna, Wiedwald Ulf, Birkel Christina S
Eduard Zintl Institute of Inorganic and Physical Chemistry, Technische Universität Darmstadt, Alarich-Weiss-Straße 12, 64287 Darmstadt, Germany.
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85282, United States.
Inorg Chem. 2022 Jul 18;61(28):10634-10641. doi: 10.1021/acs.inorgchem.2c00200. Epub 2022 Jul 1.
The research in MAX phases is mainly concentrated on the investigation of carbides rather than nitrides (currently >150 carbides and only <15 nitrides) that are predominantly synthesized by conventional solid-state techniques. This is not surprising since the preparation of nitrides and carbonitrides is more demanding due to the high stability and low diffusion rate of nitrogen-containing compounds. This leads to several drawbacks concerning potential variations in the chemical composition of the MAX phases as well as control of morphology, the two aspects that directly affect the resulting materials properties. Here, we report how alternative solid-state hybrid techniques solve these limitations by combining conventional techniques with nonconventional precursor synthesis methods, such as the "urea-glass" sol-gel or liquid ammonia method. We demonstrate the synthesis and morphology control within the V-Ga-C-N system by preparing the MAX phase carbide and nitride─the latter in the form of bulkier and more defined smaller particle structures─as well as a hitherto unknown carbonitride VGaCN MAX phase. This shows the versatility of hybrid methods starting, for example, from wet chemically obtained precursors that already contain all of the ingredients needed for carbonitride formation. All products are characterized in detail by X-ray powder diffraction, electron microscopy, and electron and X-ray photoelectron spectroscopies to confirm their structure and morphology and to detect subtle differences between the different chemical compositions.
MAX相的研究主要集中在碳化物而非氮化物（目前已发现超过150种碳化物，而氮化物只有不到15种），这些碳化物主要通过传统的固态技术合成。这并不奇怪，因为由于含氮化合物的高稳定性和低扩散速率，氮化物和碳氮化物的制备要求更高。这导致了MAX相化学成分潜在变化以及形态控制方面的几个缺点，而这两个方面直接影响最终材料的性能。在此，我们报告了替代性固态混合技术如何通过将传统技术与非常规前驱体合成方法（如“尿素-玻璃”溶胶-凝胶法或液氨法）相结合来解决这些限制。我们通过制备MAX相碳化物和氮化物（后者呈现为更粗大且更规则的较小颗粒结构）以及一种迄今未知的碳氮化物VGaCN MAX相，展示了V-Ga-C-N体系内的合成及形态控制。这表明了混合方法的多功能性，例如从湿化学获得的前驱体开始，这些前驱体已经包含形成碳氮化物所需的所有成分。所有产物都通过X射线粉末衍射、电子显微镜、电子和X射线光电子能谱进行了详细表征，以确认其结构和形态，并检测不同化学成分之间的细微差异。
