We explore the electronic structure of high-quality bismuth sodium titanate (${\mathrm{Bi}}_{1/2}{\mathrm{Na}}_{1/2}\mathrm{Ti}{\mathrm{O}}_3$) powders through a comprehensive approach combining the maximum entropy method (MEM) and Rietveld analysis of synchrotron radiation x-ray diffraction data collected at 200 K with density functional theory (DFT) calculations. The average structure is well described in the monoclinic $\mathit{Cc}$ space group rather than in the rhombohedral $R3c$ one, which is also supported by our neutron powder diffraction analysis. The MEM and Rietveld analysis provides experimental evidence of covalent Bi–O and Na–O bonding along the monoclinic $\mathit{c}$ axis. Further insights from our DFT calculations demonstrate that Bi undergoes additional displacement along the $\mathit{c}$ axis to fulfill bonding requirements; notably, the off-centered Bi forms three short bonds with oxygen atoms (2.26–2.31 Å), considerably shorter than Na–O bonds. The deviation of spontaneous polarization (${\mathbf{P}}_{\mathrm{s}}$) from ${\left[111\right]}_{\mathrm{pc}}$ is as small as 1.2 °, and the polar distortion from the rhombohedral structure (${\mathbf{P}}_{\mathrm{s}}$ // ${\left[111\right]}_{\mathrm{pc}}$) is quite small. We conclude that the covalent Bi–O bond and the resultant ferroelectricity stem primarily from the Bi $6p-\mathrm{O}3 2p$ orbital interaction mediated through Ti $3d$.

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• Chemical bonding
• Density of states
• Electronic structure
• Ferroelectricity
• First-principles calculations
• Structural properties