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Pressure-temperature phase diagrams of stage-2-4 potassium-graphite intercalation compounds deduced from anomalies in the basal plane resistivity
Umeå University, Faculty of Science and Technology, Physics.
1987 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, Vol. 35, no 15, 8231-8242 p.Article in journal (Refereed) Published
Abstract [en]

The basal-plane resistivities ρ of stage-2–4 potassium-graphite intercalation compounds (K-GIC’s) have been measured as functions of temperature T and pressure p using a contactless method. The pressure range investigated was 0–1.4 GPa. For stage-2 K-GIC (KC24) measurements were made in the temperature range 90–300 K, while for the higher-stage materials the range was mainly limited to 245–300 K. In all cases ρ increases with p through the anomalous regime near the phase transitions, whereas dρ/dp is always negative in the stable high-p (high-stage) phases. Approximate p-T phase diagrams are deduced from anomalies in ρ corresponding to the staging and in-plane order-disorder transitions, respectively. In all cases the slopes dp/dT of the phase boundaries for the high-pressure staging transitions are such that the transitions extrapolate to positive T at atmospheric p, although no such transitions have been reported. The low-p staging-ordering phase boundary of KC24 is particularly complex, involving segments with both dp/dT→0 (125<200 K) and dp/dT→∞ (T≊125 K). The p-T diagrams are compared with recent structural experiments and models. We suggest that the complexity of the KC24 phase diagram is attributable to the weakly incommensurate in-plane structure at low p and T.

Place, publisher, year, edition, pages
1987. Vol. 35, no 15, 8231-8242 p.
Keyword [en]
Graphite intercalation compounds, GIC, potassium, K, stage 2, stage 3, stage 4, electrical resistivity, contactless measurements, basal plane resistivity, anisotropy, high pressure, phase diagram, phase transformations, order-disorder transitions
National Category
Condensed Matter Physics
Research subject
URN: urn:nbn:se:umu:diva-26760DOI: 10.1103/PhysRevB.35.8231OAI: diva2:273953
Available from: 2009-10-26 Created: 2009-10-26 Last updated: 2010-02-03

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