The Fashion of X-ray Line Profile Analysis
Robert Cahn has written a wonderful book on The Coming of Materials Science. His historical insights are truly incisive. In a recent article in Sadhana he has analysed the freedom and fashion that characterise modern materials science and engineering. He has been critical of one fashion
Fashion has also occasionally led to bursts of experiment promoted simply by the availability of a newly perfected experimental technique, without consideration of what purpose the experiments can serve. An example, in which Indian groups have joined together with groups in several other countries, is the measurement of crystallographic stacking-fault densities in intensely cold-worked face-centered cubic metallic solid solutions, as a function of solute concentration and therefore of valency electron/atom ratios. The cold-working was imparted simply by filing with a fine file. The technique applied was developed by diffraction specialists in America in the 1950s: the presence of stacking faults had been shown to generate small shifts of certain X-ray powder diffraction lines. Paper after paper was published based on the purely mechanical application of this technique, without anyone ever asking: “So what?” The findings did not relate to any other property of the solid solutions, and thus did not ‘radiate’ beyond their immediate neighbourhood, as good researches always do. The moderate scepticism I mentioned in the preceding paragraph can help to counter bare fashion by asking the crucial ‘so what?’ question.
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This appears unjustified. A little historical account of the work by Indian practitioners may be apposite.
In 1950 T R Anantharaman, after graduation from the Indian Institute of Science, went to Oxford University as a Rhodes Scholar. His doctoral research was pursued under the guidance of J W Christian. It involved the determination of stacking fault densities in Cobalt by analysing their effects on X-ray line breadth and peak positions. In many ways this work was seminal. At that time TEM had not evolved. The only way to understand stacking faults was via X-ray analysis. After his return to IISc in 1957 Anantharaman pursued this line of research. P Rama Rao enrolled for doctoral research under him and obtained wonderful results. It is not surprising that when it came to the choice of B. E project, four of us- the first four rankers in the class- chose this topic in 1960. My report was considered to be excellent and Rama Rao told me that he had preserved it!
Anantharaman went to Varanasi in 1962 and took Rama Rao along with him. The work done at IISc formed a major portion of the latter’s thesis submitted to BHU. In recent times the first doctoral scholars in Metallurgy, who had obtained their Ph D degrees in 1971 from IISc, were felicitated. Actually in some sense Rama Rao’s thesis is the first one but like Karna was carried away by the waters of Ganges.
Meantime at the Trombay Centre R Krishnan began working on faults in Uranium. A celebrated paper was that of V S Arunachalam , M K Asundi and R Krishnan . It was the first to appear in Acta Metallurgica from the Indian subcontinent. I read it as a student and have always been in awe of Arunachalam, Krishnan and Acta ever since. I am told that Prof Brahm Prakash was persuaded to celebrate this publication event by hosting a lunch in the Taj Hotel.
Rama Rao’s researches were followed by those of Shrikant Lele. With his gifts for mathematics Lele took this research theme to great heights. I remember my discussions on faults in dhcp structures with him in 1968, when I had joined BHU. Lele and Rama Rao offered me coauthorship of the paper but being young and idealistic in those days, I declined stating that I am content with a mention in acknowledgments. I also remember R K Gupta and B Prasad. It must also be recorded that concurrent to this Ajit Ram Verma had established a school of research on Polytypes. His illustrious student P Krishna did beautiful work with X-rays. In a way the schools of Anantharaman and Verma had synergistic influence.
Then came rapid solidification- another wave of research swept across the country. X-ray line breadth analysis became lee of a feverish activity. There has been a minor revival in pure application of Scherrer analysis, as mechanical alloying came as the next wave.
In my view the line breadth analysis was a harbinger of conscious pursuit of metallurgical research in India. As I wrote in the citation for the IISc Distinguished Alumnus Award to Prof T R Anantharaman the present high profile of metallurgical research in India is due to his pioneering efforts. In this high profile X-ray line profile played a stellar role. It infused confidence in the faculty and students, who went on to win many laurels and established new lines of research of their own.
This line of research radiated beyond the laboratories across the nation and indeed the globe, not necessarily by replication but by the pursuit of excellence in research.