Benisek Artur, Dachs Edgar
Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Str. 2a, 5020 Salzburg, Austria.
Phys Chem Miner. 2024;51(3):23. doi: 10.1007/s00269-024-01277-6. Epub 2024 Jun 4.
The heat of mixing of some petrological relevant substitutions (i.e., Mg-Al, Si-Al, Mg-Ti, Mg-Ca, and Mg-Fe) was investigated systematically in silicates, titanates, tungstates, carbonates, oxides, hydroxides, and sulphates by density functional theory calculations (e.g., melilite, chlorite, biotite, brucite, cordierite, amphibole, talc, pseudobrookite, pyroxene, olivine, wadsleyite, ilmenite, MgWO, ringwoodite (spinel), perovskite, pyrope-grossular, magnesite-calcite, MgO-CaO, anhydrous and different hydrated MgSO). A specific substitution is characterised by different microscopic interaction energies in different minerals, e.g., the octahedral Mg-Al exchange on a single crystallographic site in pyroxene has a microscopic interaction energy that is more than twice compared to that in biotite. A comparative investigation of the heat of mixing using microscopic interaction energies on a single crystallographic site has the advantage that they are not influenced by cation ordering. They could be successfully correlated with the stiffnesses of the minerals, which in turn were scaled to the oxygen packing fraction, a parameter that is easily available for poorly investigated minerals. With this information, the interaction energies of a certain substitution can be transferred from minerals where they are well-known to mineral groups where they are less- or unknown. Using the cross-site terms and the microscopic interaction energies, the macroscopic interaction energies of the coupled substitution, e.g., Mg + Si = Al + Al, of biotite and pyroxene were calculated, which are, however, affected by cation ordering and different degrees of local charge balance, for which appropriate models are necessary.
The online version contains supplementary material available at 10.1007/s00269-024-01277-6.
通过密度泛函理论计算，系统研究了一些与岩石学相关的置换（即Mg - Al、Si - Al、Mg - Ti、Mg - Ca和Mg - Fe）在硅酸盐、钛酸盐、钨酸盐、碳酸盐、氧化物、氢氧化物和硫酸盐中的混合热（例如，黄长石、绿泥石、黑云母、水镁石、堇青石、角闪石、滑石、假板钛矿、辉石、橄榄石、瓦兹利石、钛铁矿、MgWO、林伍德石（尖晶石）、钙钛矿、镁铝榴石 - 钙铝榴石、菱镁矿 - 方解石、MgO - CaO、无水和不同水合状态的MgSO）。特定的置换在不同矿物中具有不同的微观相互作用能，例如，辉石中单个晶体学位置上的八面体Mg - Al交换的微观相互作用能比黑云母中的高出两倍多。使用单个晶体学位置上的微观相互作用能对混合热进行比较研究的优点是它们不受阳离子有序化的影响。它们可以成功地与矿物的刚度相关联，而矿物的刚度又与氧堆积分数成比例，氧堆积分数是一个对于研究较少的矿物很容易获得的参数。利用这些信息，特定置换的相互作用能可以从已知的矿物转移到研究较少或未知的矿物组中。利用跨位置项和微观相互作用能，计算了黑云母和辉石的耦合置换（例如Mg + Si = Al + Al）的宏观相互作用能，然而，这些相互作用能受到阳离子有序化和不同程度的局部电荷平衡的影响，对此需要适当的模型。
在线版本包含可在10.1007/s00269 - 024 - 01277 - 6获取的补充材料。
