First-principles investigation of the lattice vibrations in the alkali feldspar solid solution
| Autor: | Edgar Dachs, Michael Grodzicki, Artur Benisek |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
Thermodynamics
02 engineering and technology 010502 geochemistry & geophysics DFT 01 natural sciences Heat capacity Vibrational entropy KAlSi3O8 Materials Science(all) Geochemistry and Petrology CASTEP Low albite General Materials Science Softening NaAlSi3O8 0105 earth and related environmental sciences Original Paper Chemistry Infrared spectra 021001 nanoscience & nanotechnology Alkali metal Low microcline Bond length Crystallography Density functional theory 0210 nano-technology Alkali feldspar Solid solution |
| Zdroj: | Physics and Chemistry of Minerals |
| ISSN: | 1432-2021 0342-1791 |
| DOI: | 10.1007/s00269-014-0715-8 |
| Popis: | The heat capacities of Al, Si ordered alkali feldspars of different Na, K compositions were calculated using the density functional theory. The effect of the Na, K distribution, if random, ordered or clustered, on the resulting heat capacity was investigated on different cells with Ab50Or50 composition. For all compositions and distributions studied, the excess heat capacity of mixing is positive at low temperatures with a maximum at ~60 K. This produces an increasing excess vibrational entropy that reaches a constant value above ~200 K. The amount of the excess heat capacity of Ab50Or50, however, depends on the Na, K distribution. Best agreement with measured excess heat capacities is achieved, if the distribution of Na and K is either ordered or clustered. The positive excess heat capacities can be attributed to a strong softening of the acoustic and the lowest optical modes related to a strong increase of Na–O bond lengths in samples with intermediate compositions. The softening of the lowest optical mode is, however, not reflected by thoroughly measured literature IR data. Comparing calculated and measured IR spectra suggests that the resolution of the measured spectra was insufficient for detecting the lowest IR-active modes. Electronic supplementary material The online version of this article (doi:10.1007/s00269-014-0715-8) contains supplementary material, which is available to authorized users. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|
Full text from SpringerLink