In the past two decades, we have witnessed major advances in vibrational spectroscopy through a powerful combination of experiment and theory. For example, ultrafast nonlinear spectroscopy now allows us to experimentally observe the time evolution of molecular structures with femtosecond time resolution. Theoretical calculations, on the other hand, provide firm support for such experimental results and more detailed microscopic insights into molecular dynamics. In this review, we introduce our recent study on advanced vibrational spectroscopy applied to water ice and clathrate hydrate crystals. The consistency of the experimental and theoretical results provides new structural insights into these crystalline systems.

  Ferroelectrics with crystal sizes ranging from a few nanometers to several hundred nanometers (called mesoscale) significantly change their dielectric properties and anisotropy depending on their size and shape. In this article, we track the structural phase transition of a single BaTiO₃ grain using coherent X-ray diffraction and successfully visualize the three-dimensional outer shape, the domain arrangement in the tetragonal phase, and the atomic displacement distribution in the cubic phase using Bragg coherent X-ray diffraction imaging (CDI). The Bragg-CDI results suggest that the BaTiO₃ grains in the paraelectric phase exhibit grain-boundary slip, inherited from the 90° domain boundary in the tetragonal phase. Structural visualization using coherent X-rays with mesoscale sizes will contribute to our understanding of external effects on the ferroelectricity and dielectric properties of ferroelectric fine crystals.

  Metal nanoparticles undertake sintering at a lower temperature compared to their bulk counterparts, attracting great attention in industrial applications such as printed electronics. Since nanoparticles are easy to aggregate, the three-dimensional (3D) visualization of their sintering process plays a vital role in quantifying the morphological changes during heating. However, the nanoparticles are sensitive to surface contamination, resulting in poor affinity to the 3D visualization with conventional electron beam intensity because the visualization technique requires a long beam exposure time, potentially making beam induced contamination significant. In this paper, we demonstrate our developed 3D observation scheme, including advanced image processing techniques. A sample transfer system, which enables to prevent nanoparticles from being exposed to air, and an ultra-low-electron dose observation protocol prevents surface contamination during the observation. The low-signal-to-noise ratio of acquired images is compensated by the advanced image processing techniques. The obtained 3D images of nanoparticles enable to measure the neck growth and variation of particle distance in 3D during the sintering in a quantitative way.

  The automation of manufacturing processes and improvement of productivity are key challenges in the manufacturing industry. In the Floating Zone (FZ) method, a process used for the growth of crystals in the manufacturing of semiconductor wafers, operators adaptively control input parameters based on the state of the crystal growth process. The operational dynamics of crystal growth using the FZ method are complex, making automation a challenging task. This study aims to automate the control of FZ crystal growth using reinforcement learning, employing dynamics predicted by a Gaussian Mixture Model (GMM) based on a limited amount of operational data. The results from studies using an emulator program for FZ crystal growth demonstrated that the constructed control model can achieve ideal crystal shapes more effectively than human operation.

  In piezoelectric materials, there are two mechanisms for improving piezoelectric properties: the morphotropic phase boundary (MPB) mechanism and the domain engineering mechanism. In this paper, we will explain in detail the two mechanisms for improving piezoelectric properties and also the origin of piezoelectric properties. We also explain the origins of intrinsic and extrinsic piezoelectric properties. Future material design direction for development of high-performance lead-free piezoelectric materials will be explained here.

  Traditionally, piezoelectric single crystals have been fabricated mainly by melting or solution growth methods. Recently, however, the Solid State Crystal Growth (SSCG) method has been attracting attention as a promising alternative to conventional methods because of its low acoustic impedance Z₃₃, due to the presence of microscopic pores in the crystal, and easy acoustic matching with living organisms and water. Furthermore, SSCG technology has made it possible to fabricate single crystals with complex chemical compositions and incongruent melting behavior. It also has the potential to dramatically reduce production costs, compared with melt-grown crystals. This paper describes the growth mechanism of the SSCG method, outlines the general features of the production technology, and introduces examples of research on lead-based and non-lead-based piezoelectric single crystals. Among them, the latest research on the properties of Pb(Mg_1/3Nb_2/3)O₃-Pb(Zr,Ti)O₃ (PMN-PZT) single crystals fabricated by SSCG, will be described.