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Hexagonal manganese oxides RMnO$_3$ show intriguing topological ferroelectric-domain walls with variable conductivity, leading to domain wall engineering. Despite the numerous experimental studies on the polar nanoscale structures, controlling ferroelectric domains has not been sufficiently investigated. Here, we reveal the unprecedented coexistence of polar-nonpolar nanoscale domains that can be formed by substituting Ti ions in HoMnO$_3$. Unusual polar nanoscale domains are embedded in nonpolar domains with different crystallographic symmetry. This polar-nonpolar coexisting structure is naturally assembled by adjusting the lattice length during a solid-state reaction process. Furthermore, the comprehensive study reveals that the reversible microstructural change with a nonpolar-polar transition is strongly correlated with the oxygen storage properties in Ho(Mn, Ti)O$_{3+δ}$. The present results provide important insight into the nanoscale polar-nonpolar domain coexistence in functional rare-earth manganese oxides, RMnO$_3$.

This study focuses on the role of lubrication in the optimal performance design guidelines for the thrust slide-bearings in scroll compressors. The theoretical analysis of Ishii et al. showed that the minimum friction power loss in the thrust slide-bearing occurs at a certain outer radius of the friction surface. In the theoretical development, the physical thrust slide-bearing was modeled as a cylindrical thrust plate, representing the orbiting scroll, and the flat plate, representing the fixed scroll, with the same friction area as the physical bearing. The outer radius of the friction surface was varied for a fixed inner radius, where the fluid wedge angle between the sliding surfaces, due to axial loading on the thrust plate, was assumed to be constant at a small value. The average Reynolds equation by Patier & Cheng and the solid contact theory by Greenwood & Williamson were applied to calculate the resultant lubrication performance and finally the friction power loss at the sliding surface. The model showed that the friction power loss drastically decreases and then gradually increases, with increasing outer radius of the sliding surface.  The minimum value of friction power loss was about 80% lower than that of the conventional design thrust slide-bering. In order to confirm experimentally this predicted optimal lubrication performance, a thrust slide-bearing cylindrical-model submerged in a refrigerant oil SUNISO-RB68A was operated under pressurized conditions using R410A as the pressurizing gas. The pressure difference across the friction surface of the thrust bearing was fixed at 0.6 MPa, corresponding to the rated operation condition of a small cooling capacity scroll compressor. In the experiments, a special device was fabricated to maintain a constant fluid wedge angle between the friction surfaces due to the net pressure-induced elastic deformation of the thrust plate. The friction power loss at the friction surface was measured over a wide range of orbiting speeds from 1200 rpm up to 6000 rpm for a fixed orbiting radius of 3.0 mm. The resulting measured data exhibited showed the predicted tendency that the lubrication of the thrust slide-bearing is substabtially by increasing the outer radius. The friction power loss decreased with increasing outer-to-inner radii ratio of friction surface. The minimum loss occurred at an outer-to-inner radii ratio of about 2.1 for an operating speed of 3600 rpm, a significant 80% reduction relative to the usual conventional design ratio.