Materials research and development specifically for potential application in fusion energy development had its origin in the early 1970s, following the impetus of the 1973 report to the President on “The Nation's Energy Future” by Dixie Lee Ray then chairman of the U.S. Atomic Energy Commission. The first scientific conferences on fusion materials took place in the summer and the fall of 1975 at Argonne National Laboratory and at Gatlinburg, Tennessee. Argonne's international conference set a direction for the use and development of irradiation testing facilities for fusion materials which continues today.

In his keynote to the Gatlinburg meeting on “Radiation Damage and Tritium in Fusion Materials,” E.E. Kintner, then deputy director of the U.S. magnetic fusion program, spoke directly to the hearts of the materials community:

“Materials is the Queen Technology of any advanced technical system. The economics eventually depend upon the materials, the reliability depends upon the materials, and the safety depends upon the materials. I assure you that before we are through with fusion, the physicists will give way to the materials engineers as being the leading lights of fusion.”

Kintner spoke from his experience in naval and civilian nuclear power systems, with reference to the special threats of the fusion reactor environment to the integrity of materials, and from practical engineering issues in a broad sense.

Medical implant devices are being increasingly used to replace or stimulate damaged or diseased body parts. Because the body rejects any foreign matter, these components should appear, to the body, to be of natural or nonforeign material. An obvious approach is to construct prosthetics or other implant devices of “natural” material, such as bone mineral. While this can be done, in practice it is not feasible for large components since bone mineral does not possess sufficient structural or mechanical strength. Furthermore, items such as pacemakers or electrodes cannot be fabricated from bone mineral.

Since it is the surface of the medical implant that is in direct contact with the body, one solution in designing the device is to choose the bulk material for mechanical strength or other properties and to hide the surface of the device with a coating of biocompatible material. Since bone mineral is one of the most biocompatible materials known, much effort has been devoted to developing surface treatment processes to deposit this material on prosthetics and other implants.

The material bones and teeth are composed of is quite complex. Tooth enamel, itself a coating, is very durable and primarily composed of a hydrated form of calcium phosphate called hydroxylapatite (Ca10(PO4)A(OH)2), or HA. Bones are approximately 60–70% HA. However, it is not sufficient to simply produce a coating with the same chemical constitutents as HA.

Our understanding of the superconducting mechanism in the newly discovered oxide superconductors is closely connected with a detailed knowledge of the structural properties displayed by these materials. Moreover, it is important to explore possible connections between structural and superconducting properties and to establish general structural principles which can guide our search for new compounds.

We present here a survey of the structures of the recently discovered oxide superconductors. The common feature of these structures (with the exception of cubic Ba1-x Kx BiO3-y) is the presence of one or more planes of copper atoms with four strongly bonded oxygen atom neighbors in a square planar arrangement at a distance of approximately 1.90 Å (“CuO2 planes”). In some structures these planes occur in groups, with the individual planes inside a group being separated by one Y or Ca layer and the groups being intercalated by a variable number of LaO, BaO, CuO, TIO and/or BiO layers. (The intercalated CuO layer is crystallographically distinct from the “CuO2 plane”). A natural model for superconductivity which arises from these structures is that the conductivity occurs predominantly in the Cu02 planes, while the other (intercalated) layers provide in some fashion carriers and/or the coupling mechanism necessary for the superconductivity.

Since their first use about 150 years ago, silver halides have remained the primary photosensing materials in an image capturing process known as photography. Silver halides have retained their pre-eminent role despite numerous attempts to replace them with other materials. Even in the present era of electronics, conventional photography remains the most popular format for recording still images. When compared with electronic imaging, silver halide photography retains an edge in resolution, latitude, and convenience.

The current superiority and popularity of conventional photography stem from an unusual confluence of properties found in the silver halides. The ensuing articles will discuss the properties that make silver halides particularly well suited for photography. The article by L.M. Slifkin discusses the improbability of any one material having the characteristics of the silver halides. F.C. Brown describes the special electronic properties, and P.W.M. Jacobs covers ionic characteristics. C.R.A. Catlow gives us some insight into the nature of the silver halides based on their interatomic potentials. This introductory article presents an overview of the photographic process.

The theory of the photographic process has its roots in the Gurney-Mott model of latent image formation. Since it was first proposed over 50 years ago, this model has formed the basis of mechanistic thinking about photography.

BULLETIN: Is there one particular item on your agenda for MRS in 1989 that you believe needs to receive highest priority?

CHANG: Having spent the time putting together a preliminary 5-10 year plan for MRS, I find that we have several areas of priority for 1989: 1. The Headquarters needs a new computer/software system immediately in order to keep the Society moving smoothly. 2. The ratio of the Society reserve to cash flow has fallen precipitously over the last couple of years due to our rapid growth. This needs to be taken care of starting this year. 3. MRS needs to work with other materials societies to better serve the materials community at large. 4. MRS needs more activities at the Section and Chapter levels. 5. Increased visibility is needed for Journal of Materials Research in 1989.

BULLETIN: We've heard many explanations for the particularly rapid expansion of MRS membership and activities. Can you give us your perspective on what the underlying driving force behind this growth is?

CHANG: MRS is a member-driven society, and because of this many opportunities are made possible. We provide the best opportunity for members to organize new and novel materials symposia. Our meetings are structured to enhance cross fertilization among the various materials disciplines. We emphasize quality in whatever we do with our limited resources. We have a first-rate publications department that provides rapid dissemination of technical information. In short, our members are involved in every aspect of MRS operations, and their good ideas are always implemented.

The direct conversion of chemical energy in a fuel cell has been one of the most challenging technological problems since a simple hydrogen/oxygen fuel cell was first demonstrated 150 years ago by Groves at the London Institution. Aqueous electrolyte fuel cells have been successfully used in space to power electrical equipment in the Apollo spacecraft and in the space shuttle, but terrestrial applications have been principally limited to a few specialized military and telecommunication applications.

In the original concept of a fuel cell, a primary fuel (e.g., hydrogen, hydrocarbon) is reacted with oxygen in an electrochemical cell incorporating an acid electrolyte, namely:

so as to convert the free energy of oxidation (ΔG°) of the fuel to carbon dioxide and water directly into electrical energy.

Fuel cells are attractive in that theoretical thermodynamic energy/fuel conversion ratios given by the appropriate value of ΔG°/ΔH° (free energy change/enthalpy change) can be very high (e.g., ~95% for H2/O2 reaction at 298 K) compared to the limitations imposed on heat engines by the Carnot cycle efficiency, (T2−T1)/T2. However, in practice it has proved difficult to realize the high electrical/fuel conversion efficiencies promised by fuel cell systems. This is caused by problems associated with the electrochemical kinetics and/or the requirement that in the Faradaic reaction both mass and electron transfer must occur in a spatially restricted region where an electrode, an electrolyte, and one of the reacting phases (usually a gas) are in intimate contact. This region is often referred to as the three-phase boundary.

This issue of the MRS BULLETIN contains three articles relating to the general field that has come to be known as Solid State Ionics. The central feature of this area of science and emerging technology is the rapid transport of atomic or ionic species within solids, and the various phenomena, of both scientific and technological interest, that are related to it.

Attention to this area has grown greatly in recent years because of the rapidly increasing recognition of the possibility of a wide range of interesting technological applications. One example already widespread is the use of an oxygen-conducting solid electrolyte as the critical element in the oxygen sensors installed in the exhaust systems of almost all current automobiles to reduce deleterious emissions and improve the efficiency of the combustion process.

Work is under way in a number of other directions, including static and dynamic chemical sensors, solid state electrochemical reactors, low impedance selective atomic filters, new concepts for the direct conversion of heat to electricity by the use of sodium- or hydrogen-transporting cycles, a novel method for the low cost electrolysis of water at intermediate temperatures, batteries that can store greatly increased amounts of energy, ion exchange materials, solid state laser hosts, high efficiency fuel cells, electrochromic materials and configurations for both optical displays and “smart windows,” advanced catalysts, atomic reservoirs and pumps, high temperature superconductors, and possibly solid state fusion hosts.

Despite this recent attention, however, it is worth noting that interest in solids in which ionic species can move with unusual rapidity is actually not new at all. As early as 1839, Michael Faraday reported measurements on several materials that showed an unusual increase in electrical conductivity at elevated temperatures, contrary to that found in normal metals.

The propagation of small fatigue cracks differs considerably from that of long cracks in the same material. Small cracks tend to grow more rapidly than would be expected from long-crack data. Following Suresh and Ritchie, cracks are small when (1) their length is small compared to the scale of local plasticity (a linear elastic fracture mechanics, LEFM, limitation); (2) their length is small compared to microstructural dimensions (a continuum mechanics limitation); or (3) they are merely physically small. The importance of understanding the anomalously rapid growth of small cracks has been the subject of recent reviews and two specialized conferences. The impact of small cracks on component design is to force the design of highly conservative structures.

Many investigators have tried to correct LEFM to account for crack shortness. Since the early work of Kitagawa and Takahashi and Smith showing the limitations of LEFM, many procedures to modify, correct, or replace LEFM have been proposed to predict short-crack growth rates. These include mechanisms based on crack closure stress and crack deflection, elastic-plastic approaches such as the J integral, or simply semi-empirical approaches. These methods have been reasonably successful when the crack length is a few times that of the relevant micro-structural size.

The uses of polymeric materials in today's world are vast. Polymers are finding applications in the microelectronics industry as dielectric insulators and photoresists, in the aerospace and automobile industry as lightweight substitutes for metals, and in biotechnology as replacement components for bone, heart, and other organs. These are just a few of the many end uses of polymers.

Often, a polymer may have a particular, desirable property but processing of the polymer is difficult or the polymer's surface characteristics are undesirable. To circumvent such shortcomings there are several options. The first is to synthesize a new material, which is quite costly and time consuming. Alternatively, two polymers with complimentary properties can be mixed. Unfortunately, most polymer pairs are immiscible unless there are specific interactions (e.g., hydrogen bonding) between the two components. Consequently, coarse phase separation is often observed, leading to an ill-defined material. Finally, two chemically distinct homopolymers can be joined together at one point, forming a block copolymer. While phase separation may occur, the scale of the domains is restricted to the sizes of the individual homopolymers, which is typically on the tens of nanometers scale. The added advantage of this approach is that the size of the different blocks can be altered, varying the concentration of the different components. For copolymers that “microphase” separate, this variation in composition leads to a variation of the morphology of the microdomains ranging from spherical to cylindrical to lamellar.

The main concept of intelligent materials processing systems is to have online control during processing. Successful implementation of on-line control of materials processing from the total manufacturing point of view involves full integration of design, procurement, control of incoming components, manufacture, assembly, handling, packaging, and distribution.

There are three primary concerns if on-line control of materials processing is to be successful:

1. Definitive understanding of the process. Process models need to be developed which will bring forth an understanding of the processing variables.

2. Sensors that can interrogate the processes in a manner that allows for process control. Sensing is needed throughout the processing steps so that one can determine and measure various indices and the significant parameters … as borne out by physical and mathematical modeling.

3. Armed with the above, process controls are established to compare the on-line feedback obtained from sensors with the process models. When deviations are observed, measures are taken to change the processing variables so that the operation will yield a “quality” product. Intrinsic to process control is a clear definition of the properties required at the end of individual steps and the relation of the intermediate properties to those specified for the material when the total processing is completed. In fact, only in the light of a definition of the properties and the processes is it possible to define the parameters that can be monitored for on-line control.

This article provides an overview of the piezoelectric effect in all the classes of materials in which it is found to occur. This includes select materials from the categories of naturally occurring single crystals, polycrystalline ceramics, and semicrystalline polymers. Throughout this development, an attempt is made to point out the common factor for the piezoelectric effect in all these materials, namely, the presence of dipolar moieties, whose orientation brings about a net polarization in the material as a whole.

The applications of each of these classes of materials are covered briefly. Each such application has a specific value based on the aggregate properties of the material as a whole, making each material complementary rather than competitive in device applications.

Brief mention is made of the mathematics and geometry of the piezoelectric effect in order to define the piezoelectric constants by which the properties of these materials are described. The article then focuses on the basis of the piezoelectric response in synthetic polymers.

Piezoelectricity or “pressure electricity” was coined from the Greek verb “piezen,” to press, by Pierre and Jacques Curie in the 1880s during an investigation of the symmetry in crystals. In this work it was found that certain crystals, lacking a center of symmetry, produced an electrical charge when mechanically deformed. The converse effect was also found to occur, whereby applying an electric field caused the crystal to change its shape. This phenomenon was attributed to a deformation of the net internal polarization in the crystal. When no external forces are present, the centers of positive and negative charges will coincide, and there is no net polarization. The application of a stress, be it mechanical (pressure) or electrical (applied field), causes a displacement of the centers of gravity of the positive and negative charges. In the absence of a center of symmetry, the charge displacement will be nonsymmetrical and thereby produce an induced dipole moment. This dipole moment, if produced by a mechanical stress, will cause the surfaces to develop an effective charge. If an external field displaces the charges, by electrostatic attraction or repulsion, it produces a mechanical strain which causes the material to deform. The mathematical relations describing this effect were developed in the few years following their discovery, making use of tensor notation to describe the directionality of the applied stress and the resultant strain.

The papers in this edition of the MRS BULLETIN were among those presented during a workshop entitled “SAS Interfaces '87: Microscopy for the Archaeologist.” The workshop was sponsored by the Society for Archaeological Sciences at the 52nd annual meeting of the Society for American Archaeology held in Toronto, Ontario, May 1987. The Society for Archaeological Sciences is an interdisciplinary professional society for researchers involved in the broad spectrum of physical science applications to archaeology in order to promote interaction among scientists interested in different aspects of common research problems.

Archaeometry, i.e., “archaeological science,” is concerned with the physical analysis of archaeological materials and the application of techniques from the laboratory sciences to the objectives and needs of archaeology. It includes such activities as compositional analysis, reconstruction of past technologies and processes, remote sensing, paleo-environmental reconstruction, and of course, isotopic and other chronometric dating methods. Such techniques alone, however, yield results that mean little without appropriate application to anthropological problems. The chief concern of archaeologists is to choose the most appropriate analysis method to achieve results that are useful in interpreting cultural behavior. To that end, laboratory analysts need to be aware of the interests and concerns of archaeologists, and archaeologists need to be able to understand the technical advances in archaeometry to incorporate them into their research.

La2CuO4, crystallizes in an orthorhombic distortion of the tetragonal K2NiF4 structure, a so-called layered perovskite. The important question here concerns the stoichiometry of La2CuO4 prepared by various techniques. Regarding the La and Cu sites, recent neutron diffraction studies of powders have shown that the La:Cu ratio can vary from 2:1 by ≳1% in various preparations., Single crystals have been grown variously from CuO, PbO and Li2O-B2O3 fluxes. The last two fluxes incorporate some Pb and Li, respectively, into the crystals, but the cation ratio is found to be 2:1 within the accuracy of x-ray refinement.

It is also known that the oxygen stoichiometry corresponds to La2CuO4 within ≃ 1%. Extensive and precise magnetic susceptibility (χ) and other studies of powder samples showed, however, that the physical properties are extremely sensitive to < 1% changes in the oxygen content. A clear indication from electric and magnetic measurements is that the oxygen stoichiometry is always that, or richer than that, corresponding to a Mott insulator with an exactly half-filled band. Consistent with this, the stoichiometry is more properly written La2-z CuO4-y with small, positive y and z.

Several groups found that bulk superconductivity above 30 K can be produced in La2CuO4 by annealing powders or single crystals at high oxygen pressure. The weight gain in this process corresponds to producing La2CuO4.13, and these authors believe the excess oxygens go in as O-2, based on iodometric titration measurements giving the amount of [Cu-O]⊥ in the sample. Jorgensen et al. found that there is a phase separation below 320 K of La2CuO4 and the O2-loaded phase in oxygen-rich samples; the latter structure is also orthorhombic, but the position of the excess oxygens could not be determined unambiguously.

Some readers may wonder about the reasons for having two issues focus on fine particles. Hopefully, this introduction and the articles to follow will offer the necessary justification.

It is fully expected by everybody, professional or laie, that the properties of matter will change if its chemical composition is altered. It is less frequently recognized that many characteristics of materials can be dramatically affected by varying dimensions, yet countless examples in everyday life clearly demonstrate such phenomena. Consider water in droplet form. Driving in rain creates little problem, providing the car has working windshield wipers. In contrast fog, which consists of droplets of much smaller size, represents one of the major hazards in transportation. Obviously, the optical properties of the same matter have greatly altered with diminution. In another example, it is well known that finely dispersed carbon is an excellent adsorbent, a property used in gas masks and in many industries as a purifying agent. Large-sized lumps of such carbon would be useless in these applications.

The effect of particle size on properties of materials can be readily understood from a simple consideration. The total energy of any System, (Etot), consists of two contributions, the internai energy, Ei, and the surface energy, Ei.

Fracture mechanics technology is an effective tool for characterizing the rates of fatigue crack propagation. Generally, fatigue crack growth rate (da/dN) in each loading cycle can be presented as a function of stress intensity range (ΔK), where ΔK = Kmax — Kmin, Kmax and Kmin are the maximum and the minimum stress intensities, respectively. A typical fatigue crack growth rate curve of da/dN versus ΔK can be divided into three regimes, i.e., Stage I (near-threshold), Stage II (Paris), and Stage III (fast) crack growth regions, as shown in Figure 1.

Depending on the region of crack growth, fatigue crack growth behavior can be sensitive to microstructure, environment, and loading conditions [e.g., R (load) ratio = Kmin / Kmax]. In the nearthreshold region, fatigue crack growth rates are very slow, ranging from approximately 10−10 to 10−8 m/cycle. In this region, the fatigue crack growth rate curve eventually reaches a threshold stress intensity range, ΔKth, below which the crack would not grow or grow at an extremely slow rate. Typically, the value of ΔKth is operationally defined as the stress intensity range which gives a corresponding crack growth rate of 10−10 m/cycle. In the nearthreshold region, the influence of microstructure, environment, and load ratio on the rates of crack propagation is very significant.