Constructing heterophase structures of α-Cu2V2O7/β-Cu2V2O7 to enhance photovoltaic and photocatalytic properties

Abstract

α-Cu₂V₂O₇ is a rare type of negative thermal expansion material with weak photoelectric properties. Enhancing its photoelectric properties while tailoring its thermal expansion to achieve stable photoelectric conversion efficiency and improved photocatalytic properties is highly desirable. Herein, heterophase structures of α-Cu₂V₂O₇/β-Cu₂V₂O₇ are constructed by introducing Li⁺ into α-Cu₂V₂O₇. With an increasing Li content, an increasing fraction of α-Cu₂V₂O₇ is transformed into β-Cu₂V₂O₇, generating heterophase structures of α-Cu₂V₂O₇/β-Cu₂V₂O₇. The photovoltaic and photocatalytic properties are enhanced owing to the energy level matching between α-Cu₂V₂O₇ and β-Cu₂V₂O₇. The maximum values of surface photovoltage increase of Cu_1.95Li_0.05V₂O₇ are 3.7 (400 nm) and 1.4 (475 nm) relative to the pristine sample: 3.7 (400 nm) and 1.4 (475 nm) times. The maximum reduction factor of the absolute value of the thermal expansion coefficient of Cu_1.91Li_0.09V₂O₇ decreases 2.8 times compared with that of the pristine sample. The phase transition from α- to β-Cu₂V₂O₇ could relate to the introduction of heterovalent Li⁺ ions supplying fewer electrons for oxygen.