Bulk chalcogenide perovskite $\mathrm{BaZr}{\mathrm{S}}_3$ (BZS), with a direct band gap in the visible region, is an important photovoltaic material, albeit with limited applicability owing to its antiferroelectric (AF) nature. Presently, ferroelectric (FE) perovskite-based photovoltaics are attracting enormous attention for environmental stability and better energy conversion efficiency through enhanced charge separation. We report on AF-FE phases of BZS thin film using temperature-dependent Raman investigations and first-principles calculations. Origin of localized FE phase is established from an anomalous behavior of $A_g^7\sim 300\mathrm{c}{\mathrm{m}}^{-1}$ and $B_{1g}^5\sim 420\mathrm{c}{\mathrm{m}}^{-1}$ modes, which involve the vibration of atoms at the apical site of $\mathrm{Zr}{\mathrm{S}}_6$ octahedra. Additionally, $B_{1g}^1$ and $B_{2g}^2$ ($\sim 85\mathrm{c}{\mathrm{m}}^{-1}$) modes appear while antipolar $B_{2g}^1$ ($\sim 60\mathrm{c}{\mathrm{m}}^{-1}$) disappears below 60 K. Our first-principles calculations confirm that FE appears as a result of the loss of center of inversion symmetry in $\mathrm{Zr}{\mathrm{S}}_6$ due to the existence of oxygen impurities placed locally at apical sites of sulfur.

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• Electronic structure
• Ferroelectricity
• Structural properties
• Chalcogenides
• Ferroelectrics
• Functional materials
• Perovskites
• Thin films
• Band structure methods
• Density functional calculations
• Optical techniques
• Raman spectroscopy
• X-ray photoelectron spectroscopy