The grain‐growth behavior and grain‐boundary structure in titanium‐excess BaTiO3 depend on the amount of excess titanium at 1250° and 1300°3C. With excess titanium, abnormal grain growth (AGG) occurs and the grain boundaries are mostly flat or faceted with hill‐and‐valley shapes. With 0.5 at.% excess titanium, the large grains have flat {111} faces forming singular grain boundaries parallel to {111} double twins. With excess‐titanium content between 0.1 and 0.3 at.%, the abnormal grains appear to have polyhedral shapes with {100} faces. These flat or faceted grain boundaries are expected to have singular structures, and hence AGG can occur by the step growth mechanism. When the excess‐titanium content is decreased to 0, the grain boundaries become curved, indicating a rough atomic structure, and normal grain growth occurs.

When NbC–30 wt% Co powder compact is sintered at various temperatures where NbC grains (with small amounts of Co) coexist with a liquid Co–NbC matrix, the NbC grains undergo a surface roughening transition with temperature increase and the grain growth changes from abnormal to normal growth. When sintered at 1400°C, the grains are polyhedral with sharp edges (and corners) and grow abnormally because their singular surfaces move by nucleation of surface steps. When sintered at 1600°C, the edges become round, indicating the surface roughening transition. The grains still grow abnormally, but their number density is larger than that at 1400°C because of the smaller surface step free energy. When sintered at 1820°C, the grains are nearly spherical, but the flat‐surface segments still remain. The grain growth at this temperature is nearly normal because of very small surface step free energy. The surface roughening transition is reversed when a specimen initially sintered at 1820°C is heat‐treated again at 1400°C, but some grains show transition shapes with nearly flat edges and slope discontinuities (shocks).

A new general approach to the direct formation of bipolar devices from heterogeneous colloids is suggested. By using surface‐force theory and direct measurements, combinations of conductive device materials between which short‐range repulsive forces exist in the presence of an intervening liquid, and use these interactions to self‐form electrochemical junctions are identified. The inclusion of Lifshitz–van der Waals (LW) and acid–base (AB) interactions appears to be generally sufficient for the prediction of short‐range interactions. Device concepts using repulsive and attractive short‐range interactions to produce self‐organizing colloidal‐scale devices are proposed and demonstrated. A prototype self‐organizing lithium rechargeable battery is demonstrated using lithium cobalt oxide (LiCoO2) and graphite as the active electrode materials.

Grain boundaries in pure alumina powder compacts sintered at 1400°C are smoothly curved, indicating that they have atomically rough structures. When these specimens are heat‐treated at temperatures between 900° and 1100°C, a small fraction of the grain boundaries develop either hill‐and‐valley or kinked shapes with flat segments. Some of these flat boundary segments lie on the {011[Twomacr]} plane of one of the grain pairs. These grain boundaries thus appear to become singular at these temperatures. When a corundum crystal with a basal surface is sintered in alumina powder at 1400°C, all grain boundaries formed between the corundum basal surface and small grains, as well as those between the small grains, are smoothly curved, indicating their rough structure. When heat‐treated at 900°C for 3 days, about 30% of the grain boundaries between the corundum basal surface and the small grains develop kinks with flat boundary segments, and some of these flat segments lie on the basal plane of the corundum. When heat‐treated again at 1400°C, all grain boundaries are curved, indicating that they become reversibly rough. These observations show that at least some of the grain boundaries in alumina undergo roughening‐singular transitions at temperatures between 900° and 1100°C.

The grain boundaries in BaTiO3 with excess Ti of 0.5, 0.3, and 0.1 at.% sintered at 1300° or 1250°C have been examined by scanning electron microscopy (SEM), electron backscattered diffraction pattern (EBSP), and transmission electron microscopy (TEM). In the 0.1% Ti‐excess specimen, large grains growing abnormally form high‐angle grain boundaries when they impinge on each other as verified by EBSP. A large fraction of these grain boundaries are faceted with hill‐and‐valley shapes. In the 0.5% Ti‐excess specimen, large grains growing abnormally are elongated in the directions of their {111} double twins. These grains often form flat grain boundaries parallel to their {111} planes with the fine matrix grains, and the grain‐boundary segments between the large impinging grains with high misorientation angles are often also parallel to the {111} planes of one of the grains. These grain boundaries are expected to be singular. Most of the grain boundaries between the randomly oriented fine‐matrix grains in the 0.3 at.% Ti‐excess specimen are also faceted with hill‐and‐valley shapes at finer scales when observed under TEM. The facet planes are parallel to {111}, {011}, and {012} planes of one of the grain pairs and are also expected to be singular. These high‐angle grain boundaries lying on low index planes of one of the grain pairs are similar to those observed in other oxides and metals.