Gas effusion spectra of HgBa2CuO4+ delta.

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Gas effusion spectra have been obtained in the temperature range 30{endash}1000{degree}C for underdoped, optimized, and overdoped HgBa{sub 2}CuO{sub 4+{delta}} samples. We observe a large oxygen multipeak structure at high temperatures and a wide low-intensity oxygen {open_quote}{open_quote}tail{close_quote}{close_quote} at lower temperatures. The two lowest-temperature oxygen peaks are believed to originate from bonding sites for excess oxygen. The {delta} values derived from these two peaks are consistent with {delta} values derived from neutron powder diffraction (NPD). The wide low-temperature oxygen tail in the effusion spectra suggests the existence of loosely bound disordered oxygen in overdoped samples and accounts for the discrepancy between {delta} values determined by NPD and thermogravimetry analysis. Our results provide further evidence that each doping oxygen atom contributes, on average, only about one carrier to the CuO{sub 2} plane in HgBa{sub 2}CuO{sub 4+{delta}}. {copyright} {ital 1996 The American Physical Society.}