Synthesis and Characterization of Advanced Materials (1984)

This panel was concerned with the training and orientation of scientists for research in SACAM. For three reasons we focus primarily on solid-state chemistry: first, chemical synthesis and characterization are major components of SACAM research; second, solid-state chemistry is a comparatively neglected field that is much less well established than solid-state physics, metallurgy, ceramics, and materials science and, therefore, requires particular attention; and third, almost all members of the Panel (see Appendix A) and others participating in the discussion at the time of the SACAM Workshop and afterward were either solid-state chemists or were concerned with hiring and working with solid-state chemists. In this chapter, we analyze the changes that must occur if sufficient numbers of persons are to be trained in the chemical aspects of research on advanced materials. We offer a caveat concerning the restriction of our consideration largely to solid-state chemistry: it is our impression that the ignorance of chemistry among solid-state physicists and other researchers in SACAM who are not chemists is as profound and inimical to the needs of SACAM research as is the ignorance of the solid-state among chemists. Most of our suggestions for increasing awareness and enhancing the regard of chemists for the solid state could be employed, with some modifications, to deal with the ignorance of chemistry among solid-state physicists and other nonchemist researchers in SACAM.

Solid-state chemistry has not yet become well defined through long practice, in contrast to, for example, organic chemistry, even though a great variety of solid materials is indispensable to modern science and technology. Industry has borne most of the task of training people to deal with chemical problems involving solids, partly because the relevant university-based training has been inadequate and research in advanced solid materials is inherently multidisciplinary in character and so can be easily organized in an industrial laboratory.

By solid-state chemistry we mean the preparation and chemical characterization of solids; such solids are largely inorganic but not exclusively so. Solid-state chemists traditionally have dealt with semiconductors and ionic inorganic solids, but many organic materials should be included in this field.

To exploit the potential of solid structures, extensive exploration of materials with coupled electronic and crystal structures and coupled stoichiometries should be undertaken. Imaginative research is needed, and it requires sound training. Chemistry curricula focus primarily on the principles underlying the behavior and synthesis of molecular systems, with little attention to extended solids. Nevertheless, chemists will continue to play a central role in pioneering research in advanced solid materials, for scientists whose specialities are in other disciplines are unlikely to have the background and orientation required for chemical synthesis and characterization. We propose modifications of the present educational system that would lead to a more balanced division of emphasis between molecule-oriented and solid-oriented thinking.

Why is a greater emphasis on solid-state chemistry desirable? There are many phenomena displayed by crystalline and amorphous solids that are not found in molecular systems. The essence of the difference is that the long-range order in a solid gives rise to conditions and properties not found in molecular systems. Furthermore, many solids lack molecular analogs. Although the study of chemical phenomena in solids is interesting, challenging, and important, it is largely ignored in undergraduate chemistry curricula and only occasionally treated in graduate courses in chemistry. In fact, solid-state physics evolved to handle certain aspects of solid-state chemistry. The development of the solid-

state sciences has not benefited substantially from the uniquely chemical view of the interplay between structure and electronic configuration; for example, adequate and useful models of chemical bonding in solids are not available. The value of the chemical viewpoint, is verified by the contributions of chemists to fields initiated by physicists, such as spectroscopy and crystallography. The panel believes that the study of solids would benefit substantially from greatly increased emphasis on chemical modeling and theory.

The phenomena unique to solids often involve long-range and collective effects, and an appreciation of these effects requires specialized training. Superconductivity is a good example. Advances in this field are closely tied to the synthesis of novel materials, and so depend significantly on the contributions of chemists. Many of the possible binary compounds have already been explored, and the opportunities for the future lie in ternary and more complex systems requiring a high level of chemical inguenuity. Charge-density waves in the layered compounds, incommensurate lattices, and metal-to-insulator transitions illustrate the richness of behavior to be expected in compound solids. Surface studies supply an important link to such applied problems as catalysis, electroplating, and corrosion, while at the same time they provide a link between the solid-state sciences and the complementary fields of organic and physical chemistry.

Studies of solids also yield new insight into basic chemical and physical principles. Studies of mixed valence compounds, cluster compounds, nonstoichiometric materials, and extended defects are examples where the fundamental nature of the chemical bond in a solid results in behavior not predicted by traditional chemistry. Frequently such effects can be analyzed in depth most effectively with the use of solid-state probes. In addition, the diffusion of ions in solids may provide model systems that will enhance our understanding of transport processes in general while aiding in the development of novel ionic conductors for electrochemical applications.

In addition to the intellectual challenges of solid-state chemistry, there is an industrial demand for solid-state scientists. The energy industry is concerned with numerous problems related to hydrogen embrittlement, catalysis, friction, wear, solar energy (thermal and photovoltaic), and energy storage, all of which require

chemical ingenuity. The communications and computer industries need new and improved optical communications devices and high-speed computer components. The development of the next generation of optical storage, recording, and signal-processing technology will require a substantial solid-state effort. The automotive industry needs novel materials that are lightweight, durable, and do not require copious amounts of energy for their production.

Against the background of these pressures for the traning of new solid-state scientists, the magnitude of the U.S. academic effort lags behind that of other advanced countries and proportionately behind that of other scientific disciplines in the United States. This perception can be documented by the comparisons of publication rates given in Appendix B, even though Appendix B emphasizes solid-state physics. The problem seems to be particularly severe in synthetic solid-state chemistry for which the major academic centers are in Europe.

Preparative solid-state chemistry is a well-recognized and accepted discipline within chemistry departments at many European universities. The French and German university systems have a long history in the training of synthetic solid-state chemists. Unlike the great majority of chemistry departments in the United States, the areas of specialization in many European universities have included emphasis on solids rather than only solutions and gases. Examples of such university research centers can be found at Bordeaux, Nantes, Grenoble, Münster, Göttingen, Freiburg, and Stuttgart. In most cases, these centers receive government support and funding and are, at the same time, an integral part of the chemistry training programs.

In Norway and Sweden, the emphasis has been on crystal chemical problems. However, the synthesis aspect of solid-state science has also been underscored at such institutions as Oslo, Uppsala, Stockholm, and Lund. In the United Kingdom, synthesis and characterization have been noted features in inorganic chemistry at Oxford and are increasingly important in physical chemistry at Cambridge. Such encouragement within chemistry departments and by governments results in sufficient numbers of trained synthesis-oriented scientists to satisfy the industrial, governmental, and university needs of these countries.

The pattern of chemistry education in the United States generally reflects a broad overview of the physical principles and basic concepts of chemistry. At present, however, this overview understates the importance of solids and the unique chemical and physical properties of condensed phases. As a consequence, our concern here is the development of a stimulating introduction to the basic concepts of solid-state chemistry at the undergraduate level.

At the introductory level, solid-state chemistry has not been integrated into the basic curriculum, even though it is at this stage or earlier that qualified students should be exposed to the field. Few, if any, general chemistry textbooks present an adequate introduction to the chemistry of the solid state. This lack, coupled with the recent decline in the teaching of classical inorganic chemistry in introductory courses, results in the near absence of solid-state chemistry from introductory and subsequent courses. Yet a successful graduate program in solid-state chemistry is predicated on a pool of motivated students aware of the possibilities of the field. The interest in this area is illustrated in Appendix C by a list of pertinent articles from the Journal of Chemical Education during the period 1974–1981. In addition, an analysis of the coverage of solids in four popular general chemistry texts (which are said to have about 70 percent of the market) is given in Appendix D.

We believe that solid-state chemistry should be introduced, at appropriate times, throughout the student’s undergraduate experience. It is desirable to introduce this material early, preferably to freshmen, so that students can begin to gain an appreciation of solids at the outset. At the same time, a much-needed introduction to solid-state chemistry can be provided for engineers and other students who may never take another chemistry course. In addition, we recommend that, whenever possible, an introductory or advanced course in solid-state chemistry be offered, with physical chemistry as a prerequisite.

There is also an excellent opportunity to include demonstrations and laboratory experiments in solid-state chemistry in the usual chemistry courses. For example, a suitable freshman chemistry laboratory experiment is to prepare copper sulfide, which is an example of a non-

stoichiometric compound. Unfortunately, it is often presented as an example of a stoichiometric compound. At the upper level, a foundation in thermodynamics, phase equilibria, and crystallography is consistent with a sound pedagogical approach to physical chemistry and is essential to understanding solids.

Inorganic chemistry courses are a logical place to extend the presentation of solid-state chemistry, to introduce topics such as nonstoichiometric coumpounds, common structural types, and the reactions of solids, and to give practical laboratory experience. Electronic, magnetic, and optical phenomena can be abundantly illustrated by examples from the solid state. Such illustrations, in addition, provide opportunities to discuss various properties that reflect the three-dimensional nature of solids.

Of paramount concern is the development of laboratory techniques germane to the preparation and characterization of coupled and novel materials. Inorganic and integrated physical inorganic laboratories provide logical opportunities for the introduction of solid-state chemistry experiments, such as the synthesis of ferrites followed by x-ray and magnetic characterization, synthesis of and conductivity measurements on tungsten bronzes and silver halide ionic conductors, and the chemical vapor transport growth of sulfides. Experiments of this general nature require proper equipment, including furnaces, x-ray diffractometers, magnetic balances, and equipment for electrical measurements. Such equipment is generally more expensive than the equipment for traditional experiments, thus the funding of educational developments in this area requires special consideration.

Undergraduate research projects provide an excellent opportunity for the introduction of solid-state chemistry to students. This concept should also be extended to students at the high school level.

Many chemistry instructors do not have the necessary background to incorporate solid-state principles readily into the curriculum. Accordingly, we recommend the establishment of a series of summer workshops to offer in-service courses to college faculty members. These workshops would cover specific topics in detail and indicate ways that solid-state concepts might be integrated into existing courses. If the desirability of including material on solid-state chemistry in the chemistry curriculum can be demonstrated to college instructors, the demand for the inclusion of such

material in textbooks surely would follow. Another result of these tutorial workshops would be written source material for teachers wishing to include solid-state chemistry topics in their courses. Some additional suggestions are the following:

1. Inclusion of solid-state articles of a tutorial nature, as well as tested classroom demonstrations, in the Journal of Chemical Education or other generally available sources for teachers.

2. Active participation of solid-state chemists in the ACS Speakers’ Bureau.

3. Presentations by industrial speakers in academic institutions to highlight the impact of solid-state chemistry on modern technology.

A noteworthy step relevant to our first suggestion is the “State of the Art Symposium: Solid State Chemistry” in the August 1980 issue of the Journal of Chemical Education (see Appendix C).

Finally, we recommend that a clearinghouse be established to promote interaction among persons in industry and academia and persons in various departments in universities concerned with chemical apsects of condensed materials science and technology. Such a clearinghouse would solicit and publicize opportunities for summer appointments, appointments of longer duration, and joint research and training efforts. In addition, written materials that could be used for training would be exchanged. This clearinghouse might also prepare a brief description of careers in solid-state chemistry to be circulated to advisers of students. We recommend that the Solid State Subdivision of the Inorganic Chemistry Division of the American Chemical Society be requested to consider operating such a clearinghouse. The recently formed “Solid State Information Bank and Clearing House” [see J. Chem. Educ. 57, 530 (1980)] is an encouraging step in this direction, and we strongly urge that this group be supported by the chemistry and materials communities.

Graduate education of scientists in the synthesis and characterization of advanced materials requires faculty who are knowledgeable in these areas and maintain

vigorous graduate research programs. These mentors must communicate their “art” as well as the known science to students who come at present from some traditional division of chemistry. The current shortage in the United States of PhDs trained in SACAM, particularly the chemical aspects, can be traced directly to a scarcity of faculty active in this area at the major research and graduate education universities in the United States. Because of the way in which universities generally are, and probably will continue to be, organized, a research field has the best chance of flourishing if its faculty has a secure departmental home. Solid-state science can be related to a large number of university disciplines, among which are physics, materials science, metallurgy, ceramics, geochemistry, chemistry, and electrical engineering. However, for those portions of solid-state science that embody an emphasis on synthesis and characterization of advanced materials, it seems that the appropriate faculty home is in chemistry or, perhaps, materials science departments. Chemistry departments seem an attractive possibility because (a) many workers already in the field received their training in chemistry departments; (b) chemistry departments tend to be large and often can make room for an additional specialty more easily than other relevant departments; (c) chemistry is usually required of students in the other related fields, so that having solid-state specialists on chemistry faculties might increase the number of students exposed to solid-state concepts early in their careers; and (d) the science of chemistry would be enriched by the development of this important, albeit neglected, part of the discipline—the chemistry of the condensed state.

In our view, the education of people who will contribute to the advancement of solid-state science by synthesizing materials that are novel and significant in their chemical, structural, electronic, morphological, and other properties should be based on a traditional specialization, such as chemistry, physics, or metallurgy. It is the depth of understanding that permits the application of the developing principles to the solid state.

However, effective research in an interdisciplinary area such as solid-state science requires that workers in different aspects of the field and in different academic disciplines communicate closely and work together. High-quality interdisciplinary work requires the collaboration of experts in the pertinent facets of the different dis-

ciplines. This interaction is accomplished at a number of institutions through interdisciplinary materials research laboratories. Indeed, a test of the effectiveness of these laboratories might be the degree to which they have established productive interaction among faculty and students from different academic disciplines. Another aspect is ensuring that students from the relevant academic disciplines learn enough of one another’s language that they can communicate effectively and efficiently with one another. The synthesizer must be able to talk with the solid-state theoretician and with materials scientists and engineers. The technique usually used to promote this competence at an early stage is to encourage students to take courses in related areas.

Increased numbers of solid-state scientists on chemistry faculties would have a number of positive benefits: (a) training of the manpower needed for SACAM; (b) a more balanced, thus improved, program of teaching and research activities in chemistry departments; (c) increased understanding of the relationship of solid-state science to chemistry; and (d) new, basic research results, both theoretical and experimental.

There are difficulties that result from forces within and outside of chemistry departments. Because a faculty member’s career depends on judgments by his professional peers, there is pressure to obtain recognition among others in the same academic field (e.g., chemistry). A young physical chemist’s career will be advanced more if he is recognized by other chemists than if he is recognized by, for example, metallurgical engineers. (The same apparently is true in reverse for a young metallurgical engineer.) There is also pressure to obtain significant and stable research funding, which is further complicated by differences in the handling of basic and applied research in funding agencies. These problems can best be dealt with by increasing the awareness within the entire materials community of the challenges and rewards of collaborative research on advanced materials.

Most advanced-degree scientists from solid-state chemistry and materials science programs go into industrial or federally financed laboratories. These laboratories typically are organized on a multidisciplinary basis, that is, in terms of projects or programs of several

scientists and engineers whose specialties and strengths complement one another. The role of the synthetic solid-state chemist is to design and prepare materials, often materials having new compositions; the ceramist or metallurgist is concerned with mechanical and multiphase aspects; the physical scientist or physicist is primarily responsible for the physical characterization. Generally, one individual is not asked to do creative science across the whole range but rather to deal with one part in depth and to interact with colleagues in the program.

Such multidisciplinary projects require the ability to conduct research in depth, whether it is synthesis, characterization, or theory. An appreciation of those aspects of materials science that are complementary to one’s own specialty, together with their basic theory and terminology, is also necessary. A broad familiarity with the range of disciplines encompassed by SACAM is necessary but is inadequate by itself; in-depth training in some one of the SACAM disciplines is an irreplaceable requirement.

Most industrial and other multidisciplinary research and development centers are prepared to continue the training of their staff, broaden their areas of competence, furnish background in new topics, and provide opportunities to gain experience in multidisciplinary efforts. Of course, such on-the-job training represents a substantial investment and generally presupposes an initial capability to do creative work.

A key contribution in the development of many significant and useful solid-state materials has been that of the synthetic solid-state chemist who first envisioned the new material and then succeeded in preparing it. In such efforts art is involved, but, more importantly, so are an understanding of atomic behavior, electronic interactions, geometric relationships, and reaction chemistry and the skill to combine all of these. Of all roles in materials science research, that of the preparative chemist is the least well represented in terms of the numbers of academic faculty and graduating scientists. Solid-state science in general will continue to benefit from the infusion of new concepts that arise from the creation of new materials and structures. We urge the members of university physical science faculties, particularly those in chemistry, to recognize the challenging and pivotal role that solid-state chemistry must play in the future of materials science. The intellectual possibilities, by themselves, are sub-

stantial, and the needs in catalysis, energy technology, electronics, transportation, and chemical processing provide numerous exciting opportunities.

There are encouraging signs that solid-state chemistry is beginning to receive the recognition and attention that it deserves in academia in the United States. There have been numerous technical symposia on solid-state chemistry at recent ACS meetings. The first and second Gordon Research Conferences on Solid State Chemistry were held in the summers of 1980 and 1982, and a Gordon Research Conference on the Physics and Chemistry of Solids was held in the summer of 1981. The August 1980 issue of the Journal of Chemical Education contains 14 papers from a symposium on Solid State Chemistry in the Undergraduate Curriculum. The Solid State Subdivision of the ACS has created a Solid State Information Bank and Clearing House. While these are noteworthy and substantial steps in the right direction, they are only a start. Solid-state chemistry is only beginning to be recognized as an identifiable discipline in U.S. universities and among the general U.S. scientific community.