The influence of Ag and Cu on the electronic and optical properties of ZrO from first-principles calculations

Highlights

• The influence of Ag and Cu on the optoelectronic properties of ZrO is studied.

• These metallic elements improve the electronic properties of ZrO.

• These metallic elements enhance the adsorption peak of ZrO.

• ZrO shows metallic behavior in comparison to ZrO₂.

Abstract

Although zirconium oxides (Zr–O) are representative functional materials, the wide band gap of ZrO₂ limits its applications. Zirconium oxides with low concentration of oxygen maybe improve the electronic interaction in Zr–O system. However, the structure and physical properties of ZrO are not well understood. Here, the structural, electronic and optical properties of ZrO are studied by the first-principles calculations. We further study the influence of Ag and Cu on the electronic and optical properties of ZrO. The result shows that the ZrO shows better thermodynamically stale. Naturally, the structural stability of ZrO is attributed to the symmetrical Zr–O bonds. It is further found that the ZrO shows better electronic properties compared to the ZrO₂. In addition, the ZrO exhibits strong ultraviolet behavior due to the role of Zr-4d state. Furthermore, the additive Ag and Cu would improve the electronic jump between the valence band and conduction band. In particular, it is found that the alloying elements of Ag and Cu improve the storage optical properties of ZrO from the analysis of energy loss function.

Introduction

Zirconium oxides (Zr–O) are representative functional materials, which are used in various advanced technological applications from the semiconductor, solid fuel cell to the gas sensor and ultrahigh temperature ceramics [[1], [2], [3], [4]]. Over the last years, the structural feature and related properties (such as the mechanical, physical and optical properties) of the various ZrO₂ have been widely studied [[5], [6], [7], [8]]. For examples, the first-principles calculations have shown that the calculated band gap of the cubic ZrO₂ is up to 4.59 eV [9]. Therefore, the wide band gap of ZrO₂ is used in nanoelectronic and storage energy materials [10]. The recent work has shown that the experimental flexural strength, fracture toughness and Vickers hardness of ZrO₂ are up to 520.21 MPa, 7.64 MPa and 18.79 GPa [11]. Note that the alloyed ZrO₂ has high stress and better thermodynamically stable under high temperature (>1000 °C) [12]. The excellent mechanical and thermodynamic properties mean that the ZrO₂ is regarded as the high temperature ceramics. In addition, the ZrO₂ nanoparticle which has high refractive index is used in ophthalmic lenses and optical waveguides [13]. In particular, the O vacancy improves the oxygen mobility and oxygen storage capacity of ZrO₂, which is used in solid oxide fuel cells [14]. Therefore, the zirconium oxides with low concentration of oxygen (ZrO) have received great attention in recent years [15,16]. As we know, the overall properties of a solid is markedly influenced by the structural feature [[17], [18], [19], [20], [21]]. Although the cubic ZrO have been reported by Schonerg [22], the structural feature, electronic and optical properties of the cubic ZrO are unclear. In addition, alloying is an effective method to improve the physical or mechanical properties of a solid [[23], [24], [25]]. Unfortunately, the influence of alloying elements on the electronic and optical properties of ZrO is unknown.

To solve the electronic and optical properties of ZrO, in this paper, we apply the first-principles calculation to study the structure, electronic and optical properties of the perfect ZrO with cubic structure. Importantly, we further study the influence of transition metals (TM = Ag and Cu) on the electronic and optical properties of ZrO. From the symmetrical structure, one Zr atom in cubic ZrO is replaced by these transition metals. Here, we consider two transition metals: Ag and Cu. The structural feature of Ag-doped and Cu-doped ZrO is further discussed. The result shows that ZrO is a thermodynamically stable. It is found that the ZrO not only shows better electronic properties but also exhibits ultraviolet behavior. In particular, the alloying elements of Ag and Cu improve the electronic jump between the conduction band and valence band. In addition, the additive Ag and Cu are beneficial to improve the storage optical properties of ZrO oxide.