International Conference Physics.SPb/2025
Optical materials

Optical properties and crystal structure of Bi$_2$Mg$_{1-x}$Cr$_x$Ta$_2$O$_{9+\Delta}$ with pyrochlore structure

D. A. Ketova^a, M. G. Krzhizhanovskaya^b, A. A. Selyutin^b, N. A. Zhuk<sup>a

a</sup> Syktyvkar State University
^b Saint Petersburg State University

Abstract: The crystal structure and optical properties of Bi$_2$Mg$_{1-x}$Cr$_x$Ta$_2$O$_{9+\Delta}$ ($x\le$ 0.7) solid solutions with the disordered pyrochlore structure (sp. gr. $Fd\bar3m$:2) were studied. With increasing magnesium content, the unit cell parameter increases from 10.45852(1) $\mathring{\mathrm{A}}$ ($x$(Mg) = 0.3) to 10.49991(1) ($x$(Mg) = 0.7). Green samples are characterized by reflection in the green 552–558 nm and red $\sim$710 nm regions. The band gap for direct allowed electron transitions varies in the range of 2.14–2.29 eV depending on the chromium(III) ion content. Doping with chromium reduces the photoactivity of bismuth-containing pyrochlore.

Keywords: chromium, magnesium, pyrochlore, structure, optical properties.

Received: 03.05.2025
Revised: 09.06.2025
Accepted: 24.10.2025

DOI: 10.61011/OS.2025.10.61944.7997-25