Dr. Winnie Kwai-Wah Wong-Ng

Biography and Research Interests

EDUCATION:

B.Sc., 1969, Chinese University of Hong Kong. Major: chemistry, Minor: physics.

Ph.D., 1974, Louisiana State University at Baton Rouge, Louisiana. Major: Inorganic chemistry and X-ray crystallography. Minor: physical chemistry.

MEMBERS OF PROFESSIONAL SOCIETY:

American Crystallographic Association (ACA), Sigma Xi Scientific Research Society, Materials Research Society (MRS), International Center for Diffraction Data (ICDD), and American Ceramics Society (ACerS).

PROFESSIONAL EXPERIENCE:

2001-present: NIST, senior research chemist
1988-2001: NIST, research chemist

1. Energy related research

   A challenge for the US economy in the new millennium is for both emerging and mature industries to provide inexpensive, efficient, compact, safe, and environmentally friendly cutting-edge technologies for energy conversion and energy distribution applications. The goal of this project is to establish required metrology for relating properties and performance of advanced materials in energy applications to manufacturing and processing routes via analysis and understanding of phase relationship, chemistry, and microstructure. This project attempts to bring together NIST’s expertise in areas of solid-state chemistry, phase equilibria, crystallography, surface chemistry, microstructural science, and unique characterization techniques to address various near-term and long-term materials problems in the areas of thermoelectric and superconductor research. Materials of interest include powder, single crystals, films, coatings and membranes. We have extensive collaborations with outside universities, industrial and other government laboratories.    

        (1) Thermoelectric Measurements and Standards (Project Leader)

   The thermoelectric project addresses innovation of thermoelectric measurement technologies, measurement standards, materials characterization, optimization of material properties (Seebeck coefficient, resistivity, and thermal conductivity), and structure and property relationships. Materials of interest in general include metals/alloys and oxides in the form of bulk, single crystals, and films. New approaches to materials optimization include the use of thin film combinatorial techniques.  

   In recent years we have been involved in the development of low-temperature Seebeck coefficient standard reference materials, as well as a scanning tool for screening the Seebeck coefficient and resistance of films. We are also interested in developing metrology for thermoelectric fibers and for superlattice thin films. 

       (2)  Phase relations in High T_c Superconductors (HTS)

   Phase equilibrium data are critical for the development of coated conductor high T_c superconductor materials for cable, generator, fly-wheel, and transformer applications. As an integral part of a DOE R&D program, phase diagrams were determined for the (Bi,Pb)-Sr-Ca-Ca-Cu-O systems in the past. More recently, we have completed the diagrams for the Ba-R-Cu-O systems (R=lanthanides and yttrium) under atmospheric-controlled reduced conditions. Since “BaF₂” process is a promising method for producing long-length coated conductors, we have investigated the role of low-temperature melt and phase formation mechanism of the Ba₂YCu₃O_6+x high T_c phase on films prepared using the “BaF₂” process (via the e-beam evaporation and trifluoroacetate synthesis techniques).  We have also studied the interfacial interaction of high T_c phases with buffer materials. 

   In order to maximize the performance and provide for cost-effective means to fabricate second generation (2G) superconductor wires, accurate data on the phase equilibria of mixed lanthanide HTS compounds and their behavior as applied to thin films is required.  The main objective of our current work is to provide critical phase equilibrium data on the single-phase regions of mixed lanthanide HTS phases under conditions that match 2G wire processing. These phases fall in the systems Ba-R-R’-Cu-O, where R and R’ are selected lanthanides and Y.  The data will enable improvement of the superconducting properties of 2G wires through enhanced flux-pinning, leading to expeditious and cost-effective market entry. Another objective is to determine a parallel set of Ba-R-Cu-O phase diagrams as applied to films. Since phase assemblages in thin films could differ from those predicted by the bulk phase equilibria, availability of phase relations for Ba-R-Cu-O films is critical for the further development of 2G wires.

    
   

2. Crystallographic studies of technologically important high temperature oxides, including microwave, ferroelectric, magnetic materials, thermoelectrics and related materials using single crystal x-ray diffraction, and powder x-ray and neutron Rietveld refinement methods.  We have developed a NIST 1990 SRM (ruby spheres) for the calibration or single-crystal diffractometers.
3. ab initio molecular orbital calculations to understand the environmentally enhanced crack growth phenomena of silica (1988-1991).
4. Standard x-ray powder diffraction patterns of high-tech materials to be included in the x-ray Powder Diffraction File (PDF) (1988-present).

1985-1988: University of Maryland, research scientist; National Bureau of Standards, consulting scientist.

1. X-ray diffraction standard reference patterns for ceramic materials.
2. X-ray diffraction characterization of high T_c superconductor materials.
3. Certification of d-spacing Standard Reference Material (Silicon, SRM 640b).

1981-1985: International Centre for Diffraction Data (ICDD). X-ray Crystallographer and Critical Review Scientist, at National Bureau of Standards (1983-85), at ICDD Headquarters, Swarthmore, Pennsylvania (1981-83).

1. Comprehensive review of reference patterns in the Powder Diffraction File; computerized database.
2. High quality X-ray diffraction reference patterns from experimental measurements.
3. Computer software development for pattern analysis and data review.

1974-1981: Chemistry Department, University of Toronto, Toronto, Canada. Research Associate and lecturer/tutor.

1. Taught inorganic, physical chemistry and general chemistry courses.
2. Research in areas of theoretical and experimental crystallography. Theoretical studies involved investigation of intermolecular forces in solid dihalogens in order to explain their structures. Experimental X-ray crystallography research included a wide scope of compounds: organic, inorganic, organometallic and alloy, with emphasis on finding solutions to difficult problems of disordered, and twinned structures.
3. Computer software development in support of experimental and theoretical crystallographic research activities.

1969-1974: Chemistry Department, Louisiana State University at Baton Rouge, laboratory instructor, tutor and research assistant. Research work included x-ray crystallography, computer software development, and molecular orbital calculations.

Publications

Technical Talks/Presentations

Conferences & Workshops Organized/Chaired