Electron diffraction study of cobalt-rich Hf-Co

Intermetallic compounds having compositions from HfCo₄ to HfCo₈ were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr₂Co₁₁ phase in structure, has been observed in the samples with the composition ranges from HfCo₆ to HfCo₈. The phase, referred to as either Hf₂Co₁₁ or HfCo₇ phase in the literature, is actually one common phase, having a broad composition range and referred to as μ-phase in the present paper. In addition to the μ-phase, we have found coexisted fcc-Co phase and a minor Hf₂Co₇ phase. The Hf₆Co₂₃ phase has been identified in the HfCo₄ and HfCo₅ samples. Tilt-series electron diffraction revealed that the μ-phase is a one-dimensional incommensurate structure, which can be described approximately as B-centered orthorhombic with a = 0.47 nm, b = 0.82 nm, and c = 3.86 nm.