Atomistic modeling of dopant segregation in α-alumina ceramics: Coverage dependent energy of segregation and nominal dopant solubility

Abstract

Microstructural control is a key aspect in producing ceramics with tailored properties and is often achieved by using dopants in a rather empirical fashion. Atomic scale simulations could provide much needed insight but the long-standing challenge of linking simulation results on isolated grain boundaries to those measured in real ceramics needs to be resolved. Here a novel Monte-Carlo simulation method based on a microstructural model in combination with energies obtained from atomic scale energy minimization is presented. This approach allows, for the first time, the prediction of the nominal solubility of dopants (Y, La and Mg) in a ceramic purely from theory.Results compare well with segregation/precipitation data as a function of grain size, found in the literature. The method can therefore be used in developing experimental guidelines for the effective use of dopants in ceramic production, thus accelerating the development of novel materials required for innovative applications.

Effect of amount of doping agent on sintering, microstructure and optical properties of Zr- and La-doped alumina sintered by SPS

“…Mass transport in the grain boundary plane and grain boundary mobility is therefore modified. [1][2][3][4][5] As a result, the densification can either be improved or hindered due to a higher or lower diffusivity at grain boundaries. 3 Moreover, the grain size is generally finer after sintering with such doping agents due to lower grain boundary mobility.…”

“…The atomic structural environment around the segregated doping cations is similar to that it would have in known secondary phases. 4,19 Moreover, it should be highlighted that, on the one hand, the grain boundary solubility is surface dependent i.e. it depends on the grain size where finer grains will accommodate a larger amount of doping agent due to their larger surface area.…”

Segregation of anion (Cl−) impurities at transparent polycrystalline α-alumina interfaces

“…[15][16][17] The energies of the doped and undoped surfaces and GBs were calculated using the Born model for solids. The Born model describes the interatomic forces in terms of pair potentials.…”

“…16,17 To maintain the charge balance of the system one Al vacancy was created for every three Cl atoms. Our previous work on Mg doping showed that the Mg substitutional defect and oxygen vacancies are not coupled and therefore should be treated independently.…”

“…Previously it has been used successfully in our group to study the segregation behavior of several cations on alumina interfaces. [15][16][17] In the present work, the energy minimization method was used in order to calculate the segregation energy of Cl on different alumina interfaces (Section 3.2). The coordination numbers of Cl − ions on the interface were calculated in order to get an idea of the chemical environment of the ions on the interfaces (Section 3.4).…”