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Investigation of exotic stable calcium carbides using theory and experiment.

ABSTRACT: It is well known that pressure causes profound changes in the properties of atoms and chemical bonding, leading to the formation of many unusual materials. Here we systematically explore all stable calcium carbides at pressures from ambient to 100?GPa using variable-composition evolutionary structure predictions using the USPEX code. We find that Ca5C2, Ca2C, Ca3C2, CaC, Ca2C3 and CaC2 have stability fields on the phase diagram. Among these, Ca2C and Ca2C3 are successfully synthesized for the first time via high-pressure experiments with excellent structural correspondence to theoretical predictions. Of particular significance is the base-centred monoclinic phase (space group C2/m) of Ca2C, a quasi-two-dimensional metal with layers of negatively charged calcium atoms, and the primitive monoclinic phase (space group P21/c) of CaC with zigzag C4 groups. Interestingly, strong interstitial charge localization is found in the structure of R-3m-Ca5C2 with semi-metallic behaviour.

SUBMITTER: Li YL

PROVIDER: S-EPMC4432597 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Investigation of exotic stable calcium carbides using theory and experiment.

Li Yan-Ling YL Wang Sheng-Nan SN Oganov Artem R AR Gou Huiyang H Smith Jesse S JS Strobel Timothy A TA

Nature communications 20150511

It is well known that pressure causes profound changes in the properties of atoms and chemical bonding, leading to the formation of many unusual materials. Here we systematically explore all stable calcium carbides at pressures from ambient to 100 GPa using variable-composition evolutionary structure predictions using the USPEX code. We find that Ca5C2, Ca2C, Ca3C2, CaC, Ca2C3 and CaC2 have stability fields on the phase diagram. Among these, Ca2C and Ca2C3 are successfully synthesized for the fi ...[more]

PMID: 25959292

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Project description:BackgroundEvaluations of interventions to improve implementation of guidelines have failed to produce a clear pattern of results favouring a particular method. While implementation depends on clinicians and managers changing a variety of behaviours, psychological theories of behaviour and behaviour change are seldom used to try to understand difficulties in implementation or to develop interventions to overcome them.ObjectivesThis study applied psychological theory to examine explanations for difficulties in implementation. It used a theoretical framework derived from an interdisciplinary consensus exercise to code interviews across 11 theoretical domains. The focus of the study was a National Institute for Health and Clinical Excellence's Schizophrenia guideline recommendation that family intervention should be offered to the families of people with schizophrenia.MethodsParticipants were recruited from community mental health teams from three United Kingdom National Health Service (NHS) Trusts; 20 members (social workers, nurses, team managers, psychologists, and psychiatrists) participated. Semi-structured interviews were audio-taped and transcribed. Interview questions were based on the theoretical domains and addressed respondents' knowledge, attitudes and opinions regarding the guideline. Two researchers independently coded the transcript segments from each interview that were related to each theoretical domain. A score of 1 indicated that the transcript segments relating to the domain did not appear to contain description of difficulties in implementation of the family therapy guidelines; similarly a score of 0.5 indicated possible difficulties and a score of 0 indicated definite difficulties.ResultsCoding respondents' answers to questions related to the three domains 'beliefs about consequences,' 'social/professional role and identity,' and 'motivation' produced the three highest total scores indicating that factors relating to these domains were unlikely to constitute difficulties in implementation. 'Environmental context and resources' was the lowest scoring domain, with 'Emotion' scoring the second lowest, suggesting that these were likely to be areas for considering intervention. The two main resources identified as problems were time and training. The emotions that appeared to potentially influence the offer of family therapy were self-doubt and fear.ConclusionThis exploratory study demonstrates an approach to developing a theoretical understanding of implementation difficulties.

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Investigation of exotic stable calcium carbides using theory and experiment.

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Investigation of exotic stable calcium carbides using theory and experiment.

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