Synthesis, band structure, and optical properties of Ba₂ZnV₂O₈

Abstract

A novel compound Ba₂ZnV₂O₈ has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2₁/c with $a=7.9050(16)$, $b=16.149(3)$, $c=6.1580(12)\AA$, $\beta =90.49(3)$. It builds up from 1-D branchy chains of [ZnV₂O₈⁴⁻]_∞, and the Ba²⁺ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba₂ZnV₂O₈ is an insulator with direct band gap of 3.48 eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V–O bonds are mostly covalence characters and Zn–O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba–O than between the Zn–O. The refractive index of n_x, n_y, and n_z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060 nm for Ba₂ZnV₂O₈ crystal.

Introduction

During the past decades, numerous investigations have been published about the compounds found in ternary systems AO–M^IIO–V₂O₅ (A=Mg, Sr, Ba; M^II=Ni, Mn, Cu, Zn). For example, many compounds of the AM^II₂V₂O₈ family were synthesized and the magnetic properties of these compounds were studied [1], [2], [3], [4], [5]. However, the compounds with formula of A₂M^IIV₂O₈ are rarely found in these systems. To our knowledge, only Mg₂CuV₂O₈ and Mg₂NiV₂O₈ were found [6], [7]. On the other hand, the vanadates containing zinc in combination with alkaline-earth metals are inadequately studied [8], [9], [10]. In this paper, we report the synthesis of a new compound Ba₂ZnV₂O₈ (1) in high temperature solution reaction and the determination of its crystal structures by single crystal X-ray diffraction (XRD). Since many zinc compounds usually have good luminescent properties, the ultraviolet-visible diffuse reflection integral spectrum (UV-Vis DRIS) and fluorescent spectra of the title compound have been studied. Furthermore, the calculations of crystal energy band structure and optical response functions have done in order to understand the chemical bonding properties and electronic origins of optical transition for Ba₂ZnV₂O₈ crystal.