Structure and Optical Properties of LixAg1–xGaSe2 and LixAg1–xInSe2
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-04-28 |
| Journal | Inorganic Chemistry |
| Authors | Mohammed Jomaa, Vidyanshu Mishra, Dundappa Mumbaraddi, Ritobroto Sikdar, Diganta Sarkar |
| Institutions | University of Alberta, Technical Institute of Physics and Chemistry |
| Citations | 6 |
Abstract
Section titled “Abstract”Complete substitution of Li atoms for Ag atoms in AgGaSe<sub>2</sub> and AgInSe<sub>2</sub> was achieved, resulting in the solid solutions Li<sub><i>x</i></sub>Ag<sub>1-<i>x</i></sub>GaSe<sub>2</sub> and Li<sub><i>x</i></sub>Ag<sub>1-<i>x</i></sub>InSe<sub>2</sub>. The detailed crystal structures were determined by single-crystal X-ray diffraction and solid-state <sup>7</sup>Li nuclear magnetic resonance spectroscopy, which confirm that Li atoms occupy unique sites and disorder only with Ag atoms. The tetragonal CuFeS<sub>2</sub>-type structure (space group <i>I</i>4̅2<i>d</i>) was retained within the entirety of the Ga-containing solid solution Li<sub><i>x</i></sub>Ag<sub>1-<i>x</i></sub>GaSe<sub>2</sub>, which is noteworthy because the end-member LiGaSe<sub>2</sub> normally adopts the orthorhombic β-NaFeO<sub>2</sub>-type structure (space group <i>Pna</i>2<sub>1</sub>). These structures are closely related, being superstructures of the cubic sphalerite and hexagonal wurtzite prototypes adopted by diamond-like semiconductors. For the In-containing solid solution Li<sub><i>x</i></sub>Ag<sub>1-<i>x</i></sub>InSe<sub>2</sub>, the structure transforms from the tetragonal to orthorhombic forms as the Li content increases past <i>x</i> = 0.50. The optical band gaps increase gradually with higher Li content, from 1.8 to 3.4 eV in Li<sub><i>x</i></sub>Ag<sub>1-<i>x</i></sub>GaSe<sub>2</sub> and from 1.2 to 2.5 eV in Li<sub><i>x</i></sub>Ag<sub>1-<i>x</i></sub>InSe<sub>2</sub>, enabling control to desired values, while the second harmonic generation responses become stronger or are similar to those of benchmark infrared nonlinear optical materials such as AgGaS<sub>2</sub>. All members of these solid solutions remain congruently melting at accessible temperatures between 800 and 900 °C. Electronic structure calculations support the linear trends seen in the optical band gaps and confirm the mostly ionic character present in Li-Se bonds, in contrast to the more covalent character in Ga-Se or In-Se bonds.