J A Gisby

Bio: J A Gisby is an academic researcher from National Physical Laboratory. The author has contributed to research in topics: Phase (matter) & Phase diagram. The author has an hindex of 7, co-authored 16 publications receiving 685 citations.

MTDATA - thermodynamic and phase equilibrium software from the National Physical Laboratory

Abstract: In the past, the complexity of the chemical and phase equilibria established during many industrial processes has prevented the kind of in-depth understanding of their thermodynamics necessary for successful and efficient process control. Predictive thermochemistry, as embodied within MTDATA, makes such an understanding possible. MTDATA allows equilibria to be calculated for multicomponent systems of practical interest, containing many different types of phase, from critically assessed data for their component binary and ternary subsystems. Very complicated calculations can be undertaken with as many as thirty different components and 500 phases being considered simultaneously. A number of modules are incorporated for critically assessing, manipulating and retrieving the data, making various types of calculation and plotting binary, ternary, multicomponent, and predominance area diagrams. Facilities are also available for users to link the complexities of phase equilibrium calculations within MTDATA to their own software or to third party commercial software packages enabling users to simulate unit operations within an industrial plant or to integrate kinetic effects. Special derivatives of MTDATA are also now being developed to provide the sophisticated capabilities within MTDATA to non-expert users for special applications using carefully designed graphical user interfaces, which are both easy to use, and which provide output specifically designed for the particular industrial need.

The compound energy model for ionic solutions with applications to solid oxides

Abstract: The application of the compound energy model to crystalline ionic phases is discussed and compared with the regular solution model. Its application to solutions with reciprocal reactions between cations on different sublattices is discussed with special reference to oxides. Examples are taken from various solutions between spinels, including cases with vacancies and interstitials. Problems connected with the choice of a state of reference for charged components in a multicomponent solution are addressed. This paper was presented at the International Phase Diagram Prediction Symposium sponsored by the ASM/MSD Thermodynamics and Phase Equilibria Committee at Materials Week, October21-23,1991, in Cincinnati, Ohio. The symposium was organized by John Morral, University of Connecticut, and Philip Nash, Illinois Institute of Technology.

Application of Metastable Phase Diagrams to Silicate Thin Films for Alternative Gate Dielectrics

Abstract: Using the concept of metastable phase diagrams, we discuss the microstructure evolution during annealing of amorphous ZrO2–SiO2 and HfO2–SiO2 thin films for gate dielectric applications. These systems are characterized by a low solid solubility, a liquid miscibility gap and a kinetic barrier to the formation of the complex, crystalline silicate. We show that phase partitioning is expected for most compositions. Compositions within the metastable extensions of the spinodal are unstable and will spontaneously unmix in the amorphous phase upon heating. Hafnia- or zirconia-rich phases will subsequently crystallize to form HfO2 or ZrO2. Most compositions outside the metastable extensions of the liquid phase miscibility gap must phase separate above the crystallization temperature by nucleation of crystalline HfO2 or ZrO2 out of an amorphous silica-rich matrix. We present calculations of the metastable extensions of the miscibility gap and spinodal. The calculations predict that SiO2-rich compositions, investigated for gate dielectric applications, will show spinodal decomposition if they contain less than ~90 mol% SiO2 at the typical device processing temperature of 1000°C. Experimental studies of Hf-silicate films with three different compositions, between ~40 and 80 mol% HfO2 that lie inside and outside the miscibility gap, respectively, are presented. All three compositions show phase separation. Despite the different pathways of microstructure evolution, the final phase separated microstructures are similar. Experimental verification of the pathways that lead to these microstructures requires further studies.

MTDATA and the Prediction of Phase Equilibria in Oxide Systems: 30 Years of Industrial Collaboration

Abstract: This paper gives an introduction to MTDATA, Phase Equilibrium Software from the National Physical Laboratory (NPL), and describes the latest advances in the development of a comprehensive database of thermodynamic parameters to underpin calculations of phase equilibria in large oxide, sulfide, and fluoride systems of industrial interest. The database, MTOX, has been developed over a period of thirty years based upon modeling work at NPL and funded by industrial partners in a project co-ordinated by Mineral Industry Research Organisation. Applications drawn from the fields of modern copper scrap smelting, high-temperature behavior of basic oxygen steelmaking slags, flash smelting of nickel, electric furnace smelting of ilmenite, and production of pure TiO2via a low-temperature molten salt route are discussed along with calculations to assess the impact of impurities on the uncertainty of fixed points used to realize the SI unit of temperature, the kelvin.

Predictive thermochemistry and phase equilibria of slags

Abstract: It is well understood that the efficient recovery of values by pyrometallurgical processing of ores requires control of the slag chemistry. In an effort to improve the understanding of slags, a thermodynamic database on subsystems of the CaO-MgO-Fe-O-Al2O3-SiO2 system has been generated through critical assessment of the literature. Data for connecting systems of specific industrial interest are being added. The data can be combined using well-established thermodynamic principles to make calculations on the multicomponent systems of practical interest. Following a description of the calculations, this article illustrates specific applications of thermodynamic modeling to the extraction of copper, nickel, and precious metals; zinc extraction; purification of pig iron; meltdown in nuclear reactors; hot corrosion; and pollution control.

High dielectric constant gate oxides for metal oxide Si transistors

Abstract: The scaling of complementary metal oxide semiconductor transistors has led to the silicon dioxide layer, used as a gate dielectric, being so thin (14?nm) that its leakage current is too large It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (?) or 'high K' gate oxides such as hafnium oxide and hafnium silicate These oxides had not been extensively studied like SiO2, and they were found to have inferior properties compared with SiO2, such as a tendency to crystallize and a high density of electronic defects Intensive research was needed to develop these oxides as high quality electronic materials This review covers both scientific and technological issues?the choice of oxides, their deposition, their structural and metallurgical behaviour, atomic diffusion, interface structure and reactions, their electronic structure, bonding, band offsets, electronic defects, charge trapping and conduction mechanisms, mobility degradation and flat band voltage shifts The oxygen vacancy is the dominant electron trap It is turning out that the oxides must be implemented in conjunction with metal gate electrodes, the development of which is further behind Issues about work function control in metal gate electrodes are discussed

High dielectric constant oxides

Abstract: The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 nm) that its leakage current is too large. It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (κ) or 'high K' gate oxides such as hafnium oxide and hafnium silicate. Little was known about such oxides, and it was soon found that in many respects they have inferior electronic properties to SiO2 ,s uch as a tendency to crystallise and a high concentration of electronic defects. Intensive research is underway to develop these oxides into new high quality electronic materials. This review covers the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects. The use of high K oxides in capacitors of dynamic random access memories is also covered.

FactSage thermochemical software and databases, 2010–2016

Abstract: The FactSage computer package consists of a series of information, calculation and manipulation modules that enable one to access and manipulate compound and solution databases. With the various modules running under Microsoft Windows® one can perform a wide variety of thermochemical calculations and generate tables, graphs and figures of interest to chemical and physical metallurgists, chemical engineers, corrosion engineers, inorganic chemists, geochemists, ceramists, electrochemists, environmentalists, etc. This paper presents a summary of the developments in the FactSage thermochemical software and databases during the last six years. Particular emphasis is placed on the new databases and developments in calculating and manipulating phase diagrams.