Elucidating Structure–Spectral Property Relationships of Negative Thermal Expansion Zr2(WO4)(PO4)2: A First-Principles Study with Experimental Validation

Abstract

The phonon, infrared, and Raman spectroscopic properties of zirconium tungsten phosphate, Zr2(WO4)(PO4)2 (space group Pbcn, IT No. 60; Z = 4), have been extensively investigated using density functional perturbation theory (DFPT) calculations with the Perdew, Burke, and Ernzerhof exchange–correlation functional revised for solids (PBEsol) and validated by experimental characterization of Zr2(WO4)(PO4)2 prepared by hydrothermal synthesis. Using DFPT-simulated infrared, Raman, and phonon density-of-state spectra combined with Fourier transform infrared and Raman measurements, new comprehensive and extensive assignments have been made for the spectra of Zr2(WO4)(PO4)2, resulting in the characterization of its 29 and 34 most intense IR- and Raman-active modes, respectively. DFPT results also reveal that ν1(PO4) symmetric stretching and ν3(PO4) antisymmetric stretching bands have been interchanged in previous Raman experimental assignments. Negative thermal expansion in Zr2(WO4)(PO4)2 appears to have very limi...