| Abstract: | The heat capacities of synthetic single crystats of Mg2Sio4 (forsterite), Mn2Sioa (tephroite), and co2Sioa (cobalt olivine), were measured between 5 and 3g0 K using an adiabatically shieldedc alorimeter. Mg2SiOais diamagnetic,a nd its heat capacity follows a normal sigmoidal curve at low temperatures. co2sioa shows a single sharp )r-type
transition at 49.85+0102 K associated with the antiferromagnetic ordering of the magnetic moments of the Co2+ ions into a collinear spin arrangement below 49.8 K. In contrast to co2sioa, Mn2Sioah ast wo transitionsi n ci, a sharpL -typet ransitiona t 47.3g10.05K and a smaller "shoulder" in Ci centered near 12 K. The upper transition corresponds to the paramagnetic (disordered) to collinear antiferromagnetic ordering of the Mn2+ moments,
whereas the shoulder near 12 K corresponds to the change from the collinear to a canted spin structure. Our calorimetric values for the antiferromagnetic-paramagnetictr ansition temperature (N6el Temperature) are in excellent agreement with those obtained by powder magnetic susceptibility measurements, 49t2 K and 5015 K for co2Sioa and Mn2Sioa respectively.
The thermal Debye temperature, 0$, of Mg2Sioa calculated from our c$ measurements between 6.3 and 13.8 K is 768+15 K and agrees well with the elastic vaiue ofi of 758 K based on the mean sound velocity calculated from the room temperature elastic stiffness constants (ci:) of Graham and Barsch.
At 298.15K (25"c) the molar heat capacitiesa re 118.6,1 28.7, and 133.4J /(mol . K) and the molar entropiesa re 94.11-r0.101, 55.910.4a nd,1 42.6-+0.J2l (mol . K) respectivelyf or Mg2SiO4M, n2SiOaa, nd Co2SiOa. |
| Genre: | Article |
| ProdID: | 70043517 |
| Citation Author: | Robie, Richard A.; Hemingway, Bruce S.; Takei, Humihiko |
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| Citation End Page: | 482 |
| Citation Issue: | 5-6 |
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| Citation Language: | English |
| Citation Larger Work Title: | American Mineralogist |
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| Citation Month: | 6 |
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| Citation Publisher: | Mineralogical Society of America |
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| Citation Search Results Text: | Heat capacities and entropies of Mg2SiOa, Mn2SiOa, and Co2SiOa between 5 and 380 K; 1982; Article; Journal; American Mineralogist; Robie, Richard A.; Hemingway, Bruce S.; Takei, Humihiko |
| Citation Start Page: | 470 |
| Citation Volume: | 67 |
| Citation Year: | 1982 |
| Type: | citation/reference |
| Text: | Heat capacities and entropies of Mg2SiOa, Mn2SiOa, and Co2SiOa between 5 and 380 K; 1982; Article; Journal; American Mineralogist; Robie, Richard A.; Hemingway, Bruce S.; Takei, Humihiko |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DOCUMENT): | http://www.minsocam.org/ammin/AM67/AM67_470.pdf |
| Date Other: | Thu, 1 Jul 1982 00:00 -0500 |
| Publisher: | Mineralogical Society of America |
