In advanced device technologies such as microelectromechanical systems (MEMS), nanoscale electronics, optoelectronic components, and piezoelectric devices, the demand for enhanced mechanical, electrical, and optical performance together with high reliability continues to grow. In response, a variety of functional thin-film materials have been developed; among them, Pb(Zr,Ti)O₃ (PZT) thin films with high piezoelectric coefficients have emerged as key materials for realizing highperformance sensors and actuators. However, residual stress within thin films can adversely affect device reliability, performance, and lifetime. This tutorial paper provides a practical and step-by-step guide to residual stress analysis using X-ray diffraction (XRD) based on the sin²φ method. As a representative case study, we quantitatively analyze the in-plane residual stress of a PZT thin film deposited on a flexible metal-foil substrate. Residual stress was evaluated using X-ray diffraction (XRD) in combination with the sin²φ method. The present analysis is expected to deepen understanding of residual-stress behavior in thin films and to inform stress-aware design and reliability optimization of PZT-based devices

Rietveld refinement has become an essential tool for the quantitative analysis of crystal structures in polycrystalline systems using X-ray diffraction data. This tutorial paper focuses on the background, case studies, and practical implementation of Rietveld refinement using the open-source software PROFEX. Key structural parameters, such as lattice constants and phase fractions, can be quantitatively extracted through full-pattern fitting. Case studies involving compositional variation, electric fields, temperature changes, and battery cycling demonstrate the broad applicability of Rietveld refinement in materials science, energy storage, and catalysis. A step-by-step procedure for performing Rietveld refinement is presented using Bi_1/2Na_1/2TiO₃ perovskite ceramic as an example, providing guidance on software installation, preparing crystal structure information files, performing Rietveld refinement, evaluating results using R-factor and χ² values, and summarizing the results. This tutorial aims to improve understanding and accessibility of Rietveld refinement for researchers seeking to investigate structure-property relationships in complex material systems.

In functional materials, in situ experimental techniques as a function of external stimulus (e.g., electric field, magnetic field, light, etc.) or changes in ambient environments (e.g., temperature, humidity, pressure, etc.) are highly essential for analyzing how the physical properties of target materials are activated/evolved by the given stimulation. In particular, in situ electric-field-dependent X-ray diffraction (XRD) measurements have been extensively utilized for understanding the underlying mechanisms of the emerging electromechanical responses to external electric field in various ferroelectric, piezoelectric, and electrostrictive materials. This tutorial article briefly introduces basic principles/key concepts of in situ electric-field-dependent XRD analysis using a lab-scale XRD machine. We anticipate that the in situ XRD method provides a practical tool to systematically identify/monitor a structural modification of various electromechanical materials driven by applying an external electric field.