The Raman bands of Ba2CuO3 at 563 cm-1 and of Hg-1201 at 571 and 591 cm-1 were observed on a HgBa2CuO4+σ (Hg-1201) crystal under laser irradiation with a power of 2 to 3 mW/μm2 and at a short acquisition time of 1 s, indicating the formation of Ba2CuO3 on thesurface of the Hg-1201 crystallite. The Ba2CuO3 decomposed to BaCuO2 under higher laser irradiation. We suggest that a two-step chemical reaction occurred on the surface of the crystal. First, a HgO segment is drawn out of the crystallite, leaving a vacant plane. The crystallite then collapses, the upper part displaced by a 2 and b 2, and newe Ba-O bonds form. In this manner, the HgBa2CuO4+σ on the surface of a crystal turns into a layer of Ba2CuO3.
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