Ligand induced stabilization of native and non-native phases of MnSe

 

 

Rashmi, Sri Sivakumar^{, #, ┴, ,}*, Raj Ganesh S. Pala^{, #,}*

Materials Science Programme, Indian Institute of Technology, Kanpur, 208016, India

# Department of Chemical Engineering, Indian Institute of Technology, Kanpur, 208016, India

┴ Centre for Environmental Science and Engineering, Indian Institute of Technology, Kanpur, 208016, India

Centre for Nanoscience and Soft Nanotechnology, Indian Institute of Technology, Kanpur, 208016, India

*Corresponding authors: srisiva[at]iitk.ac.in, rpala[at]iitk.ac.in

 

Manganese selenide (MnSe), p-type magnetic semiconductor, is one of the important members of transition metal chalcogenide family and has various applications such as battery, supercapacitors, solar cell and sensors. It is found in three phases such as Rocksalt, Wurtzite and Zincblende with space group FMm (225), P6₃mc (186) and F3m (216). Octahedrally coordinated Rocksalt structure is a thermodynamically stable phase and called native phase whereas the tetrahedrally coordinated Zincblende and Wurtzite polymorphs are called non-native phase. Study of native and non-native (polymorphism) phases of materials have been large interest due to their structure-dependent optical, catalytic and electronic properties. To study the properties of native and non-native phases, it is essential to stabilize both the phases however, the stabilization of non-native phases is challenging compared to native phases. Among various methods (e.g. temperature, dopant, ligand and high-pressure) ligand based stabilization is one of the important method due to control of size, shape and temperature. In the ligand induced stabilization, the functional groups such as carboxylic group, amino group and olefinic group of ligands (oleic acid, oleylamine, stearic acid, octadecylamine and octadecene) play an important role. In order to understand the role of different functional groups for the stabilization of native as well as non-native, we performed density functional theory (DFT) simulation and experiments. Our DFT finding suggested that along with the acetate, the olefinic group plays an important role in the stabilization of the (Wurtzite) non-native phases however only amino group is sufficient to stabilize the native phase. Bonding nature of these functional groups on surfaces has been confirmed by partial density of states and Bader charge analysis. These DFT findings was further validated by experiments by using different ligands such as oleic acid (carboxylic and olefinic groups), oleylamine (amine and olefinic groups), octadecylamine (amine group) and stearic acid (carboxylic group). X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ¹H NMR and high-resolution transmission electron microscopy (HRTEM) have confirmed that oleic acid stabilized Wurtzite (non-native) phase, oleylamine and octadecylamine stabilized Rocksalt (native) whereas stearic acid and octadecene favored none of them.