Gas effusion spectra of HgBa2CuO4+δ

Gas effusion spectra have been obtained in the temperature range 30 endash 1000 degree C for underdoped, optimized, and overdoped HgBa2CuO4+δ 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 δ values derived from these two peaks are consistent with δ 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 δ 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 CuO2 plane in HgBa2CuO4+δ. copyright 1996 The American Physical Society