dc.contributor.author | Damby, David E. | |
dc.contributor.author | Llewellin, E.W. | |
dc.contributor.author | Horwell, Claire J. | |
dc.contributor.author | Williamson, Benedict J. | |
dc.contributor.author | Najorka, J. | |
dc.contributor.author | Cressey, G. | |
dc.contributor.author | Carpenter, M. | |
dc.date.accessioned | 2016-02-12T12:04:49Z | |
dc.date.issued | 2014 | |
dc.description.abstract | Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al(3+) and Na(+) for Si(4+); similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time, the dynamics and energy changes associated with the α-β phase transition in volcanic cristobalite are investigated using X-ray powder diffraction with simultaneous in situ heating and differential scanning calorimetry. At ambient temperature, volcanic cristobalite exists in the α form and has a larger cell volume than synthetic α-cristobalite; as a result, its diffraction pattern sits between ICDD α- and β-cristobalite library patterns, which could cause ambiguity in phase identification. On heating from ambient temperature, volcanic cristobalite exhibits a lower degree of thermal expansion than synthetic cristobalite, and it also has a lower α-β transition temperature (∼473 K) compared with synthetic cristobalite (upwards of 543 K); these observations are discussed in relation to the presence of Al(3+) and Na(+) defects. The transition shows a stable and reproducible hysteresis loop with α and β phases coexisting through the transition, suggesting that discrete crystals in the sample have different transition temperatures. | en_GB |
dc.description.sponsorship | Christopher Moyes Memorial Foundation | en_GB |
dc.description.sponsorship | Natural Environment Research Council (NERC) | en_GB |
dc.identifier.citation | Vol. 47 (4), pp. 1205 - 1215 | en_GB |
dc.identifier.doi | 10.1107/S160057671401070X | |
dc.identifier.grantnumber | NE/C518081/2 | en_GB |
dc.identifier.uri | http://hdl.handle.net/10871/19775 | |
dc.language.iso | en | en_GB |
dc.publisher | International Union of Crystallography / Wiley | en_GB |
dc.relation.url | http://www.ncbi.nlm.nih.gov/pubmed/25242910 | en_GB |
dc.rights | This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited. | en_GB |
dc.subject | cristobalite | en_GB |
dc.subject | phase transitions | en_GB |
dc.title | The α-β phase transition in volcanic cristobalite | en_GB |
dc.type | Article | en_GB |
dc.date.available | 2016-02-12T12:04:49Z | |
dc.identifier.issn | 0021-8898 | |
dc.identifier.eissn | 1600-5767 | |
dc.identifier.journal | Journal of Applied Crystallography | en_GB |