Thermodynamic and structural variations along the olivenite-libethenite solid solution

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00023272%3A_____%2F23%3A10136214" target="_blank" >RIV/00023272:_____/23:10136214 - isvavai.cz</a>

Result on the web

<a href="https://ejm.copernicus.org/articles/35/157/2023/" target="_blank" >https://ejm.copernicus.org/articles/35/157/2023/</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.5194/ejm-35-157-2023" target="_blank" >10.5194/ejm-35-157-2023</a>

Result language

angličtina

Original language name

Thermodynamic and structural variations along the olivenite-libethenite solid solution

Original language description

Many natural secondary arsenates contain a small fraction of phosphate. In this work, we investigated the olivenite-libethenite (Cu2(AsO4)(OH)-Cu2(PO4)(OH)) solid solution as a model system for the P-As substitution in secondary minerals. The synthetic samples spanned the entire range from pure olivenite (Xlib=0) to libethenite (Xlib=1). Acid-solution calorimetry determined that the excess enthalpies are non-ideal, with a maximum at Xlib=0.6 of +1.6 kJ molMINUS SIGN 1. This asymmetry can be described by the Redlich-Kister equation of Hex= Xoli.Xlib [A+B(XoliMINUS SIGN Xlib)], with A=6.27 +- 0.16 and B=2.9 +- 0.5 kJ molMINUS SIGN 1. Three-dimensional electron diffraction analysis on the intermediate member with Xlib=0.5 showed that there is no P-As ordering, meaning that the configurational entropy (Sconf) can be calculated. The excess vibrational entropies, determined by relaxation calorimetry, are small and negative. The entropies of mixing also show asymmetry, with a maximum near Xlib=0.6. Autocorrelation analysis of infrared spectra suggests local heterogeneity that arises from strain relaxation around cations with different sizes (As5+/P5+) in the intermediate members and explains the positive enthalpies of mixing. The length scale of this strain is around 5 Å, limited to the vicinity of the tetrahedra in the structure. At longer length scales (ALMOST EQUAL TO15 Å), the strain is partially compensated by the monoclinic-orthorhombic transformation. The volume of mixing shows complex behavior, determined by P-As substitution and symmetry change. A small (0.9 kJ molMINUS SIGN 1) drop in enthalpies of mixing in the region of Xlib=0.7-0.8 confirms the change from monoclinic to orthorhombic symmetry.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

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OECD FORD branch

10504 - Mineralogy

Project

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Continuities

V - Vyzkumna aktivita podporovana z jinych verejnych zdroju

Publication year

2023

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

European Journal of Mineralogy

ISSN

1617-4011

e-ISSN

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Volume of the periodical

35

Issue of the periodical within the volume

2

Country of publishing house

DE - GERMANY

Number of pages

13

Pages from-to

157-169

UT code for WoS article

000956217400001

EID of the result in the Scopus database

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