A stripe-type magnetic structure and related orbital ordering are universally observed in iron-based superconductors. As an exception, the quasi-one-dimensional ladder material BaFe2Se3, which shows pressure-induced superconductivity, exhibits a block-type antiferromagnetic ordering. The research of the electronic and structural properties in BaFe2Se3 at ambient conditions is important to reveal the origin of multiorbital superconductivity. Here, we report the temperature-dependent crystal structure of BaFe2Se3, combining optical second harmonic generation experiments and neutron diffraction measurements. We elucidate the crystal structure with the Pmn21 space group in the lowerature phase below Ts2=400 K, further above the Néel temperature. This lowerature phase loses spatial inversion symmetry, where a resultant macroscopic polarization emerges along the rung direction. The transition is characterized by block-type lattice distortions possibly accompanied by polar orbital ordering.
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