2. Materials and Methods
To provide an overview of the state of the art of a specific topic, an approach such as bibliometric analysis is deemed appropriate [
2]. Additionally, to ensure the integrity and validity of a bibliometric analysis, specific guidelines and approaches should be followed [
3,
4]. In this study, we adopted the guidelines presented in [
4,
5] and used the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) protocol to increase reproducibility and accuracy of the documents identified and selected [
6]. To carry out this study, the open-source R (v. 4.3.3) package “Bibliometrix” (v. 4.2.1) was utilized [
5]. To identify documents relevant to the topic, the Scopus and Web of Science (WoS) databases were used due to their high impact, the large number of scientific documents from established sources that they contain, and the ability to extract information that can be used by the Bibliometrix tool [
7,
8]. To identify relevant documents, a detailed query was used: (“artificial intelligence” OR “ai”) AND (“materials science” OR “materials engineer” OR “materials science and engineering” OR “materials characterization” OR “materials test*”). The query used keywords related to AI and material sciences. As the field of AI has undergone drastic advancements in the last few years, only English documents from 2019 to 2023 were searched for at a topic level (e.g., title, abstract, and keywords). As 2024 was still ongoing during the performance of this study, the documents published in 2024 were not included as, by missing data from a whole semester, the outcomes for 2024 would not have been valid. The detailed document processing flowchart is presented in
Figure 1.
Specifically, 889 documents (Scopus: 603 and WoS: 286) that are relevant to the topic were identified in May 2024. The removal of duplicates was performed both automatically through Bibliometrix as well as manually, and 237 duplicates were found and removed. Hence, the initial screening for eligibility involved 652 documents. Some documents (Reasons 2–7) were removed due to their being proceedings books (10), editorials (10), retracted documents (3), errata (1), and letters (1). Additionally, using the keywords and automatically searching within the titles and abstracts of the documents, 209 documents were removed as they were out of the scope of this study and did not focus on the use of AI in the greater context of materials science. Thereafter, the remaining 418 documents were manually processed and assessed for eligibility through the examination of their full text. The inclusion criteria were for a document to focus on, examine, or use AI or its subfields in materials science, materials engineering, material characterization, or materials testing. Through this process, 148 documents were removed as they did not meet the inclusion criteria. As a result, the document collection examined and analyzed in this study consisted of 270 documents.
It is worth noting that Scopus and WoS are considered two of the most impactful databases and most appropriate to conduct bibliometric analyses [
7,
8], and their indexed documents are highly relevant to the topic. Nonetheless, the use of only two databases can be regarded as a limitation of this study. Additionally, although bibliometric analysis enables us to present a descriptive representation of the current state of the art, it does not allow for an in-depth analysis of each document. To address this, we analyzed the most impactful documents arising from the analysis. Biases can also be introduced in such studies. To counter that, we opted to use the most widely used databases which contain the documents most relevant to the topic, we selected to use a tool widely utilized and specialized for this task, and, in addition, we included all types of documents. Therefore, the metrics presented in this study derive directly from the datasets generated from the two databases.
3. Results
The descriptive statistics of the document collection examined in this study are presented in
Table 1. Specifically, the document collection consisted of 270 documents which were published from 2019 to 2023 in 208 sources. Despite the documents examined being published in the last 5 years, the average age of the documents was 2.27, which in combination with the high annual growth rate of 48.02% highlights the importance of, and interest in, the use of AI in materials science. This increase is in line with the advancement of the field of AI. A total of 1350 authors from 50 countries contributed to the documents of the collection examined. Each document received 28.16 citations on average and was created by 5.86 co-authors on average. Only 20 documents (7.41%) were created by a single author. Additionally, collaborations among stakeholders from different countries and continents were observed to have an international co-authorship rate of 14.07%. The majority of documents (49.3%) were published as research articles in journals, while a large number of documents (34.4%) were review studies. In total, 35 documents (13.0%) were published in conferences/proceedings and 9 documents (3.3%) were published as book chapters.
As the field of AI is advancing, its adoption and use in different domains is increasing. The high annual growth rate of 48.02% highlights that the use of AI to enrich and transform materials science is no exception to this trend. This fact can be further validated by the annual scientific production presented in
Figure 2 and
Table 2. Specifically, the number of documents being published that are relevant to the topic is increasing annually, something that is expected to continue in the future. Most of the documents were published in 2023 (freq.: 96, pct.: 35.6%), followed by 2022 (freq.: 74, pct.: 27.4%), which is a drastic increase when considering that only 20 (7.4%) relevant documents were published in 2019. These findings are in line with the increasing interest in AI and its being widely adopted and examined. Moreover, the documents from 2019 followed by those published in 2020 have the largest mean total number of citations per document (MeanTCperArt), with 70.6 and 61.97, respectively. When examining the average total number of citations received per year (MeanTCperYear), which reveals the impact and relevance of a document over time, the documents published in 2020 (12.39 MeanTCperYear) present the highest MeanTCperYear, followed by those published in 2019 (11.77 MeanTCperYear).
Furthermore, the sources in which the documents were published were examined using Bradford’s law, which “estimates the exponentially diminishing returns of searching for references in science journals” [
5,
9]. In particular, the documents were classified into three clusters, with Cluster 1 consisting of the most impactful sources. Cluster 1 was composed of 31 sources (14.9%) in which 90 documents (33.3%) were published. Cluster 2 consisted of 88 sources (42.3%) in which 91 documents (33.7%) were published. Cluster 3 was composed of 89 sources (42.8%) in which 89 documents (33.0%) were published. The most impactful sources based on Bradford’s law are presented in
Table 3. Specifically, ranks 1–6 of Cluster 1 belonged to the following sources:
Advanced Materials (number of published documents: 7 and impact factor: 27.4),
MRS Bulletin (number of published documents: 5 and impact factor: 4.1),
Nanomaterials (number of published documents: 5 and impact factor: 4.4),
Materials (number of published documents: 4 and impact factor: 3.1),
MRS Communications (number of published documents: 4 and impact factor: 16.8), and
WIREs Computational Molecular Science (number of published documents: 4 and impact factor: 1.8). The remaining sources had fewer than three relevant documents published.
Table 4 depicts the most impactful sources based on their published documents’ h-index and total number of citations on the topic. It is worth noting that only three sources (
Advanced Materials,
MRS Communications, and
MRS Bulletin) started publishing documents on this topic in 2019.
The most impactful documents that greatly contribute to the development of this topic can be identified by examining the total number of citations, the total number of citations per year, and the normalized total number of citations received globally. The related outcomes are presented in
Table 5. Focusing on the total number of citations, it can be observed that the top 10 documents have all received over 100 citations, with most of them having over 200 citations. The study of [
10] (382 citations) has received most citations, followed by the study of [
11] (322 citations). When focusing on the total number of citations received per year to identify the document’s annual influence, the study of [
10] (76.4 citations received per year) and the study of [
12] (71.75 citations received per year) were the only ones that received over 70 citations per year. When considering the normalized total number of citations which eliminates temporal biases, thus allowing for a fairer comparison between older and recent studies, the studies of [
11] (6.59) and [
10] (6.16 normalized total citations) are the most influential ones, followed by the studies of [
13] (5.23 normalized total citations), [
11] (5.2 normalized total citations), and [
14] (4.89 normalized total citations).
Moreover, when taking the corresponding author’s country into account, the countries whose authors focus on this topic can be identified. Specifically, when considering the number of documents published, the United States (74 documents), China (57 documents), Germany (14 documents), India (11 documents), and South Korea (11 documents) emerge as the countries whose authors have contributed the most documents related to the use of AI in materials science. The related information is presented in
Table 6. This may be due to the fact that the United States and China are among those that invest the most in research and innovation worldwide (according to data from the Global Innovation Index 2023 Ranking [
20]) and that, furthermore, both countries lead the world in AI-research investment strategy [
21].
Focusing on the total number of citations received, the countries whose authors have contributed the most impactful documents can be identified as shown in
Table 7. In particular, the United States (2582 citations), China (1582 citations), Germany (685 citations), South Korea (381 citations), and Canada (319 citations) are the countries whose authors have received the most citations. However, it should be noted that authors from countries such as Austria and Portugal have contributed a single but impactful document. Hence, the average number of citations received per document should also be considered. Furthermore, considering the international co-authorship rate (14.07%) and the fact that authors from different countries and continents are actively collaborating, the country collaboration network is displayed in
Figure 3.
To obtain a better understanding of the thematic map of the topic, the keywords, both keyword-plus and author keywords, were also examined and are presented in
Table 8. Based on the outcomes, the role of AI and its subfields (e.g., machine learning, deep learning, neural networks) in materials science is highlighted. This role becomes more evident when considering the keyword co-occurrence network presented in
Figure 4. Specifically, three main clusters arose. Cluster 1 (blue color) refers to machine learning and deep learning and includes terms such as learning algorithms, data mining, forecasting, etc., which are being more widely used in materials science. Cluster 2 (red color) highlights the role of AI and its versatile nature, which enables it to be used for different purposes and in different domains (e.g., drug discovery, simulations, automation, industrial research, etc.). Cluster 3 (green color) highlights the key aspects which the integration of AI in materials science can affect, such as prediction, optimization, design, discovery, generation, etc. Some smaller clusters related to different types of neural networks and material properties are also noticed but are less impactful overall. The keywords were also used to examine the trend topics presented in
Figure 5. Even during the five-year period (2019–2023) explored in this study, some trends emerged. Specifically, the focus shifted to automation, material discovery, and machines during 2020–2022, and thereafter (2022–2023) more emphasis was placed on machine learning, natural language processing, graph neural networks, materials science, and properties. The focus on artificial intelligence and its role in materials science has become more obvious since 2021. Additionally, since 2020 emphasis has been placed on drug discovery.
When clustering the documents using document coupling and focusing on the keywords, six main clusters emerged which can be seen in
Figure 6. Specifically, the first cluster was related toin-vitro, qsar, and bacteria-driven microswimmers, the second cluster was associated with neutral networks, deep learning, and deep neural networks, and the third cluster was related to artificial intelligence, materials science, and artificial neural networks. The remaining three clusters revealed a higher impact and were related to density-functional theory, materials informatics, and scaling relations (cluster 4), design, discovery, and optimization (cluster 5), and machine learning, deep learning, and artificial intelligence (cluster 6). Furthermore, focusing on the use of keywords, the thematic map revealed eight themes as can be seen in
Figure 7. Four themes were characterized as emerging or declining themes and refer to (i) memory, dynamics, and networks; (ii) in-vitro, density, and hydroxyapatite; (iii) differential phase contrast; and iv) irradiation, whereas the remaining four themes were characterized as motor themes and refer to (i) AI, natural language processing, and chemistry; (ii) machine learning, materials science, and deep learning; (iii) industrial research, additives, and biomedical applications; and (iv) design, neural networks, and optimization. The thematic evolution was also examined focusing on the periods of 2019–2021 and 2022–2023. The specific outcomes can be seen in
Figure 8. The greater emphasis on artificial intelligence and related technologies as well as the focus on specific aspects of materials science during 2022–2023 were observed.
4. Discussion
Based on the findings, it can be concluded that although AI can significantly enrich and transform materials science, its integration in materials science is still in its early stages. Nonetheless, given the significant annual growth rate (48.02%) of related documents being published in recent years (2019–2023), and with the majority having been published in the last two years (63.0%), the importance of the topic is highlighted and is expected to be further advanced in the near future. Sources of various types, such as journals, conferences, and books, have been utilized to publish relevant documents, with 31 sources (14.9%) being regarded as highly impactful. Authors from 40 countries have contributed to the creation of the documents examined. Several international collaborations, even across continents, emerged. This fact highlights the recency and significance of the topic. Authors from the United States, China, Germany, and South Korea have both the largest number of published documents on the topic and the highest number of citations received.
Furthermore, to obtain a better understanding about which categories of materials science AI is most applied in, the existence of specific keywords within the title, abstract, author keywords, and keywords-plus of each of the 270 documents was examined. It should be mentioned that due to the nature of the topic, a document can belong to more than one category. The eight areas of materials science used were presented in Extremera et al. [
22] and are based on the classification provided by the Materials Research Society [
1]. The outcomes are summarized in
Table 9. Specifically, the materials science area in which AI is most being applied in is “Materials structure, processing, and properties” (70.0%). Particular emphasis is also placed on its use in “Electronics, optics, and quantum” (29.3%) as well as in “Materials computing and data science” (29.3%). The use of AI in “Structural and functional materials” (25.9%), “Material characterization” (24.1%), “Carbon-based nanocomposite materials and applications” (22.2%), and “Energy and sustainability” (21.5%) is also being examined. Finally, the use of AI in the area of “Biomaterials and soft materials” (12.2%) is examined in the context of materials science to a lesser extent. These results provide a clearer, albeit estimated, representation of the areas of materials science where AI is most being examined and applied, which is consistent with previously presented results on virtual reality (VR) applications in Extremera et al. [
22].
As an estimate, it can be seen in
Figure 9 that there are fields in which many applications of AI are being found, especially in engineering. Similarly, it can also be seen that in the field of MSE there is hardly any significant progress, so this shows the potential that AI still has in this field and the margin for research that exists. In spite of this, there are recent studies that predict a strong development of this sector in the coming years. Thus, one can highlight the work of Choudhary et al. [
23], which shows the potential of deep learning in working with images and spectral data of large da-tabs materials; Liang et al. [
24] assemble machine learning models to predict the creep behavior of concrete; in this field of mechanical properties, Ni and Gao [
25] apply deep learning to identify elastic modulus, thus providing a less costly method than traditional non-destructive evaluation (NDE) techniques; Kennedy et al. [
26] evidence the application of AI in the research and development of applications related to both acoustics and mechanics; Morgan and Jacobs [
27] highlight the importance of creating open-source software packages to advance the implementation of AI in MSE; and even in the paper by Hanxun et al. [
28], new concepts for materials which can respond autonomously in real time to certain external inputs (decision-making materials) are planned; on the other hand, Orosa et al. [
29] trained neural networks to predict interior environments from the design of interior covering materials, thus designing an original methodology to optimize these environments.