A Mother of Crystallography, Helen Megaw (1907-2002).

[NNadir]

My first interest in a class of crystals known as perovskites came when I was considering certain oxygen transporting crystals in connection with a thermochemical water splitting concept I was dreaming up. These crystals were doped oxide perovskites, and back in 2015 I actually compiled a spreadsheet based list, searchable by compositional elements of around 150 of these known substances and the rates at which oxygen permeates through them.

There are much better thermochemical cycles than the one I thought up, but dreams die hard, and even bad ideas have value.

Speaking of bad ideas, there is a lot of talk these days about perovskite solar cells which involve lead chemistry.

I oppose these solar cells, but that's another matter.

I came across a solar cell perovskite paper today - one really can't avoid them since so many are written - and it got me to thinking about the class of perovskites in general, and how the world came across them, and I learned that their structure was first elucidated by a great woman scientist, Helen Megaw, who worked in x-ray crystallography and who was one of the leading scientists in this field throughout the 20th century.

Here's a nice little paper published in her honor: Helen D. Megaw (1907–2002) and Her Contributions to Ferroelectrics (IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control M. Glazer, , vol. 68, no. 2, pp. 334-338, Feb. 2021)

Some excerpts:

Helen D. Megaw was a pioneer in crystallography where her work on perovskites had a great impact on the research on ferroelectrics and beyond. In addition to her scientific discoveries, she was also a mentor and role model to many people in the field. This article celebrates her life and the numerous scientific contributions to the structures of ferroelectric materials.

Helen Dick Megaw was born on June 1, 1907, into a most distinguished and influential Northern Irish family. Her father, Robert Dick Megaw, was a famous Chancery Judge in the High Court of Justice of Northern Ireland and an Ulster politician. Also, her uncle, Major-General Sir John Wallace Dick Megaw, was a director of the Indian Medical Service, while one brother built the Mersey tunnel (in Liverpool, U.K.), the Dartford tunnel (London), the Victoria underground line (London), and Battersea (London) power station. Another brother, Sir John Megaw, was a Lord Justice in the Court of Appeal, and one of her sisters researched diet and health in the 1930s and marriage laws in Uganda in the 1950s. A most extraordinary family background!...

...One of her aunts was secretary to the Mistress of Girton College, Cambridge (one of the only two Cambridge Colleges at the time exclusively set up for women: the College like all others in Cambridge now accepts both men and women) and Helen’s ambition was to study there. She won an exhibition1 to the College in 1925 but for financial reasons decided to go to Queen’s University, Belfast. The next year, she won a scholarship, and this time, it proved possible for her to take up a place at Girton. Initially, she had intended to read Mathematics, but she had enjoyed Chemistry at school, and on her teacher’s advice, she opted for Natural Sciences so that she could study both science and mathematics. She thought that the regulations required her to study three subjects, and she planned to study chemistry, physics, and mathematics. However, her Director of Studies, Miss M. B. Thomas, explained that she was required to study three experimental subjects (mathematics being an optional extra), and she advised Megaw to choose mineralogy as her third experimental subject. Had Helen known that she could have selected geology instead of mineralogy, she would have opted for geology, and, in all probability, she would not have become a crystallographer! ...

...So, it was that she became a research student under the renowned, and some would say infamous, John Desmond Bernal, investigating the thermal expansion of crystals, and the atomic structure of ice and the mineral hydrargillite (a hydroxide of aluminum). One of Bernal’s students at the same time was the young Dorothy Crowfoot, later to become famous as the Nobel Prize winner Dorothy Hodgkin, and Helen and Dorothy became firm friends...

... Bernal was a stimulating influence on Helen and happily confirmed her interest in crystals. Her choice of crystallography was a wise one, because it was the one scientific discipline then, thanks principally to W. H. and W. L. Bragg, which had already established itself as a place in which both men and women could engage on an equal basis, and she never, or rarely, was aware of any form of discrimination. She started work on the structure of the mineral hydrargillite, a form of Al(OH)3. Fig. 2 shows a photograph of a model of its crystal structure. Although rather rough, having seen better times, this model was her first crystal model constructed with help from Dorothy Hodgkin in 1934. Megaw’s main Ph.D. work with Bernal was a study of the crystal structures of ice. Helen’s accurate and demanding investigation of ice and heavy ice showed that the hydrogen atoms were involved in bonding between two oxygens. She and Bernal surveyed the known structures of hydroxides and of water and concluded that there were two types of hydrogen bonds. In one kind, found in ice, the hydrogen oscillates between two positions, each being closer to one of the oxygen atoms than the other. In the other type, the hydrogen is bonded more strongly to one of the two oxygen atoms. In honor of her discoveries of the nature of ice, an island in Antarctica was named Megaw Island in 1962...

... In 1934, Helen spent a year with Prof. Hermann Mark in Vienna and then moved to work briefly under Prof. Francis Simon at the Clarendon Laboratory, Oxford. This was followed by two years of school teaching before taking up a position at Philips Lamps Ltd. in Mitcham in 1943. It was here that she worked out the crystal structure of a significant industrial material, barium titanate, which is used in capacitors, pressure-sensitive devices, and in a variety of other electrical and optical applications. This material, which crystallizes in the so-called perovskite structure, belongs to the class of materials known as ferroelectrics, discovered initially around 1935. Because of its strategic military importance, much of the work was secret, and Helen was only allowed to publish her work on the structure provided that she did not mention its useful properties! This structure is so famous and important that Helen’s name is permanently associated with it and with perovskite structures in general. In the ferroelectrics community, Helen’s contributions are notably recognized, and her book Ferroelectricity in Crystals published in 1957 was the first of its kind and soon became a classic text (Fig. 4)...

Figure 4:



The article says that she gave the idea to Bernal, based on her work on ice crystals, to explore the x-ray crystallography of proteins, a field that has enormous implications in the discovery of pharmaceutical compounds and the treatment of disease.

I'm kind of glad I stumbled on her. A very interesting scientist...

[calimary]

1. Impressive!

And so far above my “pay grade”!

Women like her are inspirations.