סמינר כימיה פיסיקלית ואנליטית

מרצה: Esti Ritov

09-09 May 2021 @ 12:30

מיקום: HYBRID (up to 25 people in the Seminar room, green pass holders only) Join Zoom Meeting at:

Preparation and physical characterization of bulk and exfoliated alloyed transition metal phosphorus trichalcogenides (MnxZn1-xPS3)

In the latter half of 20th century, transition-metal phosphorus trichalcogenides (MPX3) were extensively studied towards understanding their layered crystal structure and intercalation properties. At that time, they emerged as potential candidates for cathodes in lithium batteries. With the beginning of the era of two-dimensional (2D) materials, MPX3 materials arouse a new interest in the scientific community, motivated by searching for a new class of two-dimensional materials with diverse electronic, optical and magnetic properties.

Transition metal sulfide (MPS3) compounds (M=Cr, Mn, Fe, Ni, etc and X=S, Se and Te) crystallize into a monoclinic layered structure, which corresponds to C2/m space group. Single layer of MPS3 consists of a cation metal (M2+) plane structured as a honeycomb array, sandwiched between (P2S6)-4 anion planes, while the adjacent layers are held by weak van der Waals interactions. The attractiveness of the MPS3 family stems from their diversity of original physical and chemical properties, which are not generally encountered in other layered materials – enfolding both semiconducting and magnetic properties, robust chemical stability at ambient conditions, and tunable magnetism via cation exchange by using divalent magnetic metal cations such as Mn2+, Fe2+, Ni2+, which paramagnetic at high temperatures and undergo a transition to antiferromagnetic state on cooling.

In this work, a series of mixed-metal (alloyed) bulk compounds of MnxZn1-xPS3 (0≤x≤1) are prepared by vapor-sublimation method. The structural and crystallographic properties as well as the atomic compositions are determined by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The first part in this work focuses on utilizing the MnxZn1-xPS3 binary-metal system for studying: i) The nature of magnetic ion (MnII) interaction in a diamagnetic host ZnPS3 (diamagnetic), as function of the magnetic ions content x, i.e. alloying degree. ii) The impact of the alloying degree on optical properties of the system. The crystallographic similarity of ZnII and MnII, near equal ionic radii (Zn2+= 0.74 Å, Mn2+ = 0.8 Å), and the difference in magnetic properties of ZnPS3 (diamagnetic) and MnPS3 (antiferromagnetic) make the cation substitution series Mn1Zn1-xPS3 a good system for controlling and modifying the magnetic and optical properties. These aims are fulfilled by using a wide variety of experimental techniques, such as Raman and FTIR spectroscopy, superconducting quantum interference device, electron paramagnetic resonance, photoacoustic spectroscopy and more.

The second part elaborate on the liquid exfoliation of MnPS3 and ZnPS3 using for N-methyl-2-pyrrolidone solvent, for achieving few-layers dispersions. The optical and physical properties are investigated via transmission electron microscopy, Raman, electron paramagnetic resonance, UV-VIS and PL measurements.