Linking Grain Boundaries and Grain Growth in Ceramics

Abstract

The macroscopic properties of most materials are strongly influenced by grain size. In ceramic materials the microstructure usually results from the sintering process. Understanding the basic mechanisms of grain growth on an atomic length scale in ceramics would be beneficial to tailor the microstructure for improved macroscopic performance of devices. A method is presented using grain growth experiments to select samples for closer examination of grain boundaries with transmission electron microscopy. The growth experiments are used to identify temperatures were changes at grain boundaries occur at high temperature. Subsequently samples of interest are investigated using transmission electron microscopy (TEM) methods. The correlation between TEM results and changes in grain growth behavior can be used to gain closer insight into the processes occurring during grain growth at an atomic length scale. Strontium titanate is used as model system to demonstrate the combination of growth experiments with TEM results. Normal grain growth shows two distinct drops in growth rate in the temperature range between 1 300 and 1 425 °C, independent of the A‐site to B‐site stoichiometry of the perovskite. In previous studies a high preference for grain boundary planes oriented parallel to the 100 direction of one of the adjacent grains was found in the high temperature regime. This study shows that the preference does not exist in the low temperature regime possibly explaining the change in grain growth rate.

Growth of single crystalline seeds into polycrystalline strontium titanate: Anisotropy of the mobility, intrinsic drag effects and kinetic shape of grain boundaries

“…4). Strontium titanate is known to show a grain growth anomaly with the grain growth rate decreasing between 1350 and 1425°C [17][18][19][20][21], hence at 1380°C a smaller grain size than at 1350°C is expected. After 90 h the microstructure is stagnant.…”

“…In this paper we present a suite of measurements and combined analyses of grain growth of large, oriented single crystals into polycrystals which are themselves undergoing grain growth, to provide additional insights into the origins of growth rate transitions in strontium titanate [17][18][19][20][21]. The initial orientation of the interface between the single crystal and the polycrystal can be set by polishing the single crystal at a particular orientation before joining and the polycrystalline matrix provides the driving force for growth of the single crystal at any point in time at temperature.…”

“…Such analyses can lead to testable hypotheses for the possible causes of the observed ''grain growth anomaly'' in undoped strontium titanate: in strontium titanate, the grain growth constant does not show the classical Arrhenius-type behavior, but instead shows a decrease in growth rate in the temperature range of 1350°C-1425°C with increasing temperature, followed by an increase again as temperature increases [17][18][19][20][21]. Although no dopants are introduced that might lead to the observed behavior, transitions in grain boundary structure, stoichiometry, and coupling may occur with temperature alone and could account for this behavior.…”

“…A temperature-induced change in grain boundary energy/ faceting was proposed as an explanation of the non-Arrhenius behavior in strontium titanate [20]; it is well known that both grain boundary energy and mobility are anisotropic in strontium titanate [34,35,[37][38][39]; a temperature induced faceting/defacetting transition close to 1590°C is known as well [40,41]. Bäurer et al suggested a decrease of the relative grain boundary energy of low mobility boundaries with increasing temperature [20].…”

“…Bäurer et al suggested a decrease of the relative grain boundary energy of low mobility boundaries with increasing temperature [20]. This transition would result in an increasing frequency of low energy, low mobility grain boundaries which would lead to a changing distribution of curvatures in the system and a corresponding decrease of the grain growth constant.…”