The "Future Materials Exploring Initiative - Engineering for Diverse Stable Phases -" is an R&D strategy aimed at exploring materials which meet with sophisticated requirements such as improved performance and functionality, coexistence of multiple functions, and compatibility of conflicting functions, by substantial expansion of scopes for materials search into areas that have never been explored. Here, we boldly pursue novel methods for creation of materials, using diverse techniques such as an increase of number of constituent elements, high-entropy effect, utilization of diverse stable phases including metastable ones, and process control to stabilize thermodynamically unstable structures. We expect a large paradigm shift in materials creation by formulating guidelines and principles for design of new materials and processes through above-mentioned efforts.

In recent years, there is a growing demand and expectations for higher performance and advanced functionality of materials and devices to cope with diverse social requirements. These include the massive introduction of renewable energy and advanced energy management aimed at reducing CO₂, the realization of Society 5.0 through comfortable mobility with autonomous driving and utilization of IoT/AI, and the lessening of a product' s environmental impact during manufacturing and at their use. In addition to better performance, there is currently a need to achieve the coexistence of multiple functions and the compatibility of conflicting functions, such as achieving high strength and toughness in ultra-lightweight materials and high electrical conduction with low heat conduction in thermoelectric conversion materials.

However, it becomes progressively difficult to develop new materials in the respective application fields within the traditional scope of material-design using simple element configurations or the easily realized stable crystalline phases. Therefore, the target of our research must be expanded to include unexplored materials with complex compositions and unexplored stable phases that hold unknown potential. Further, recent intensified competition in materials development strongly requires reduced development period for both materials design and manufacturing processes, covering materials research and actual production. Therefore, it becomes important to formulate new guidelines for new materials creation across different application fields.

In addition, recent developments in materials informatics (MI) should be paid attention for efficient materials design. They include data sciences such as first-principles calculations, big data analysis, machine learning, and Bayesian inference, as well as efficient experiments (high-throughput experiments) utilizing robots and combinatorial approaches toward simultaneously manufacturing materials with diverse compositions. Application of these new approaches to researches of unexplored materials which have been difficult to obtain with conventional experiment methods is expected to lead to efficient selection of composition and structure with the target function as well as efficient formulation of a manufacturing process for production of a stable material meeting these requirements. Therefore, it is required to expand the research areas for materials creation to unexplored materials groups to meet with requirements for sophisticated functions, and challenge is required for new materials production in the expanded area.

Future R&D challenges include expanding the scope of material search, visualizing reaction processes and dynamically controlling reaction pathways throughout the manufacturing process, and achieving a target stable phase through the use of process control means. The following is a description of the R&D that should be conducted.

• (1) Expanding the scope of material search

  We must clarify the roles of such primary factors as constituent elements and bonding states that have a great effect on the basic properties and functions of materials, as well as the role of each element among multiple-elements structures and the complementary roles of added elements. The use of theoretical calculations and materials informatics and the application of high-throughput experiments will be essential for clarifying the roles of these factors. Also important is the clarification of roles in the manufacturing process related to reaction pathways, such as raw materials, precursors, additive elements, increased entropy due to an increased number of elements, strain, and the like.

  We must share the various data obtained through these efforts and the results of analysis through machine learning and other means in the form of a database that can be used beyond the fields of application. It is important to extract the primary factors and organize their roles and effects as scientific principles in order to present these results in a form that researchers can logically comprehend, model and use in simulations. Moreover, it will be desirable to formulate new guidelines for investigating and designing new stable phases across all areas of application.

• (2) Visualizing reaction processes and dynamically controlling reaction pathways during the manufacturing process

  Visualization in in-situ observations and measurements (operando measurements) to grasp the state of the reaction product, atmosphere, phase transitions, and the like is essential for producing target stable phases at will. We must develop process equipment with the capability for such operando measurements, in-situ monitoring equipment capable of detecting the reaction product and atmosphere, and measurement techniques capable of tracing dynamic changes in the stable phases. Areas that are difficult to visualize in operando measurements should be complemented with theoretical calculations of reactions and estimations of reaction mechanisms from process-related data accumulated to date.

  It is essential to understand the reaction process under various conditions and dynamic changes in stable phases from a scientific perspective using these technologies and measurement data and to formulate new scientific theories that treat the reaction processes and changes in stable phases integrally. Even when there is a strong tendency for other stable phases to appear preferentially during the reaction process, we need to explore reaction pathways for acquiring the target stable phase and develop precise-control approaches.

• (3) Achieving the target stable phase through use of process control means

  Since some materials in a stable phase may become unstable in the operating environment due to low energy barriers to other stable phases, an approach toward further stabilizing the target stable phase must be formulated. Applying process control means, such as forcibly arranging atoms during epitaxial growth using a crystal substrate that possesses specific lattice constant and surface structure, or rapidly lowering the temperature and pressure from a high-temperature, high-pressure state, is effective in some cases for achieving the target stable phase.

Implementing the R&D described above will require integrated R&D from materials design to manufacturing process design (reaction pathway design), operando measurements, property evaluation, and data science. It will be particularly important to acquire guidelines for new materials design and process design that transcend the fields of application. The research should be carried out under a leader overseeing the entire operation with this goal firmly in mind. While such research may be conducted through a network-like arrangement connecting all research institutes involved, the formation of research centers is more preferable from the viewpoint of developing measurement equipment and manufacturing process equipment, nurturing interdisciplinary personnel, and conducting efficient R&D. By including researchers and technicians of industries versed in the various challenges of application fields and also researchers in various basic fields at universities and national research institutes, we hope to train human resources that are familiar with both academic research and application-oriented research.

An approach to creating new functional materials by expanding the scope of material search into unexplored materials and dynamically controlling various stable phases remains disjointed even from a global perspective. It is important that we establish these research areas promptly in Japan. To so do, we must form new communities spanning materials design, process design, measurements, and data science and expedite the enactment of policies aimed at accelerating this R&D.