Crystal-chemical origins of the ultrahigh conductivity of metallic delafossites.

Despite their highly anisotropic complex-oxidic nature, certain delafossite compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed that of Au, while their low-temperature electronic mean-free-paths reach an astonishing 20 µm. It is widely accepted that these materials must be ultrapure to achieve this, although the methods for their growth (which produce only small crystals) are not typically capable of such. Here, we report a different approach to PdCoO2 crystal growth, using chemical vapor transport methods to achieve order-of-magnitude gains in size, the highest structural qualities yet reported, and record residual resistivity ratios ( > 440). Nevertheless, detailed mass spectrometry measurements on these materials reveal that they are not ultrapure in a general sense, typically harboring 100s-of-parts-per-million impurity levels. Through quantitative crystal-chemical analyses, we resolve this apparent dichotomy, showing that the vast majority of impurities are forced to reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly pure (∼1 ppm impurity concentrations). These purities are shown to be in quantitative agreement with measured residual resistivities. We thus conclude that a sublattice purification mechanism is essential to the ultrahigh low-temperature conductivity and mean-free-path of metallic delafossites.

The individual, environmental, and organizational factors that influence nurses' use of facial protection to prevent occupational transmission of communicable respiratory illness in acute care hospitals.

BACKGROUND: Communicable respiratory illness is an important cause of morbidity among nurses. One of the key reasons for occupational transmission of this illness is the failure to implement appropriate barrier precautions, particularly facial protection. The objectives of this study were to describe the factors that influence nurses' decisions to use facial protection and to determine their relative importance in predicting compliance. METHODS: This cross-sectional survey was conducted in 9 units of 2 urban hospitals in which nursing staff regularly use facial protection. RESULTS: A total of 400 self-administered questionnaires were provided to nurses, and 177 were returned (44% response rate). Less than half of respondents reported compliance with the recommended use of facial protection (eye/face protection, respirators, and surgical masks) to prevent occupational transmission of communicable respiratory disease. Multivariate analysis showed 5 factors to be key predictors of nurses' compliance with the recommended use of facial protection. These factors include full-time work status, greater than 5 years tenure as a nurse, at least monthly use of facial protection, a belief that media coverage of infectious diseases impacts risk perception and work practices, and organizational support for health and safety. CONCLUSION: Strategies and interventions based on these findings should result in enhanced compliance with facial protection and, ultimately, a reduction in occupational transmission of communicable respiratory illness.