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Writer's pictureDale DeBakcsy

Helen Dick Megaw and the Dynamic Lives of Inorganic Molecules.

In 1941, the first patent was filed for a hot new product that stood to revolutionize the electronics field - it was a capacitor that employed barium titanate (BaTiO3), one of a small family of molecules that exhibit an array of properties so astonishing that for years the full extent of their characteristics was considered a classified secret by the US government. For years, we knew that barium titanate was capable of some really cool things, but it wasn’t until Helen Megaw (1907-2002) bent the power of her crystallographic techniques to investigating the molecule that we learned the full why of the matter, and opened up thereby a whole new way of looking at the ferroelectric compounds that played such an important role in electrifying the modern world.


Megaw was born in Dublin to a family of astonishing achievement. Her parents, uncles, aunts, and siblings earned distinction in the realms of law, medicine, engineering, nutrition, and politics, and it will therefore come as little surprise that young Helen was given every encouragement and opportunity to fully realize the startling potential of her brain. By the time she was eighteen, she was already well on her way to an interest in chemistry, having been hooked by the world outlined in William Henry Bragg’s 1915 X-Rays and Crystal Structures, in which he presented some of the astounding results of the first years of x-ray crystallography research. 


Crystallography was not only fascinating in and of itself as a means of opening up the innermost geometries of the world’s molecules, but it was also a field in which women played a uniquely prominent role. In 1924, the year before Megaw began her studies at Queen’s College, Belfast, Kathleen Lonsdale began her crystallographic career as part of Bragg’s research group, a position from which she encouraged other women to pursue work in the field. Megaw was perfectly situated to take part in this eruption of new research, but her joining the ranks of the inorganic crystallographers was largely a matter of chance. When she transferred from Queen’s College to Girton in 1926 she decided to study the Natural Sciences, which required three specialties. She chose mathematics, physics, and chemistry, but was then informed that the three specialties had to be experimentally based, and so she fatefully replaced mathematics with mineralogy, creating a powerful and unique combination of interests and competencies that would form the particular path of her career. 


Megaw graduated in 1930 and was told, like so many women of her era were, that there was no real future for her in physics graduate studies, and she was shunted over to the Department of Mineralogy where she worked alongside future Nobel winner Dorothy Crowfoot Hodgkin in the lab of JD Bernal. Bernal was a charismatic and intellectually omnivorous individual as famous for the breadth of his insights as he was for his views on open marriages. Fortunately for Megaw, his predatory gaze fell on Crowfoot, rather than herself, and she was able to carry on her research without the omnipresent threat of sexual advances from her superior. That research, on the structure of ice and heavy ice (ice featuring heavier isotopes of hydrogen in its water molecules) uncovered not only interesting new insights into how the hydrogens in water form hydrogen bonds with the oxygens of nearby molecules, but also established new crystallographic techniques for locating hydrogens in molecules. 



For this work, Megaw was awarded her PhD in 1934, which was quite possibly the worst conceivable moment in European history to enter into the world as a woman with a highly specialized scientific doctorate. The Depression was in full swing, science departments were contracting under lack of funding, and if anybody was going to be getting a job in that climate, it was men of established reputation, not women fresh from their graduate work. A Hertha Ayrton Research Fellowship allowed her to stretch her studies another couple of years at Vienna’s Chemisches Institut, but by 1936 the writing was on the wall, and for the next seven years she made her living as a physics teacher at first a girls’ high school then grammar school, doing what research she could during the school breaks. 


It was not, then, until 1943 that Megaw could devote herself fully to scientific research again, when she began work as a crystallographer for the Philips Mitcham Works Research Laboratory. This was two years after the first patent for a barium titanate capacitor had been filed, and by some shipping mistake, one of the devices made its way into the hands of Philips Mitcham, where it fell to Megaw to study how its structure might hold a key to its rich array of chemical properties. 


It is now time, then, to get to know this marvelous little molecule that sparked a lifelong research interest for Megaw and an entire industry devoted to exploiting the capacities of it and its molecular cousins. Barium titanate is what we call a perovskite - a molecule of formula ABO3 which forms crystals similar to those of the mineral perovskite (I know - did they have to use the same name for the category and the specific mineral? Did they really?). In these crystals the A atoms sit on the corners of each unit cell, and the B atoms sit in the center. This structure gives the perovskites the potential for some unique properties - of the 32 different crystal classes there are out there, the perovskites belong to one of the very few that are pyroelectric (they generate electricity when exposed to temperature change), piezoelectric (they generate electricity when physically distorted), and ferroelectric (capable of generating their own electric potential even without an outside electric field pushing them to do so). 


These multiple attributes, along with others discovered in the ensuing decades, make the perovskites ideally suited for a number of electric devices - their ferroelectric capacities allowed electrical engineers to design capacitors around them that were much more compact than anything available previously. Their piezoelectric capacity made them for years an important component of microphone technology. Their ability to hold information about their history in their current state (a form of “inorganic memory”) makes them useful as sensors of exquisite sensitivity. And that’s just scratching the surface. The question, then, is, where does all this robust array of talents come from?


Megaw devoted her crystallographic skills to providing an answer, publishing her first paper on the subject in 1945. The multiplicity of the properties of barium titanate, she found, is the result of the slipperiness of that central titanium ion, which at low temperatures moves away from its central position, creating a cascade effect that lines up the ions in the crystal into a permanent state of polarity even without an electric field inducing one. BaTiO3 is capable of assuming four different crystal symmetries depending on where that titanium ion shifts, and elucidating how these shifts occur in barium titanate and its perovskite cousins would form a major part of Megaw’s work in the 1940s and 1950s, culminating in her 1957 book Ferroelectricity in Crystals which became a classic in the field, establishing the power of crystallography as a tool in mineral research just as Rosalind Franklin had demonstrated its power as a tool in organic research through her analysis of DNA and protein structures. 


Speaking of which, the power of Megaw’s analysis of the perovskites served as her entry to the very beating heart of crystallographic research, the Cavendish Laboratory, which she joined in 1946, and where she remained until her retirement in 1972. Crystallography legend William Lawrence Bragg was there, as were Francis and Crick, but while that pair focused on the trendy organic molecules that would make them household names and Nobel laureates, Megaw kept resolutely to the world of crystals and minerals, starting up a research interest in feldspars that began in the 1950s and would stretch into the 1960s, as she attempted to make the world as aware of the dynamism under their seeming permanence and stability as she had that of the perovskites. 


Feldspars make up about sixty percent of the Earth’s crust, so understanding their structure is, you know, kinda important, and yet a number of simplistic beliefs about them had persisted into the 1950s largely because, compared to the world of proteins, DNA, and carbohydrates that most crystallographers flocked to, the mysteries of the Earth’s crust seemed less enticing. Traditional microscopes revealed a world of uncomplicated uniformity, but Megaw suspected there was more at work than met the optical eye, and brought the power of x-ray methods to their investigation. When she did, she found a world of disorder lurking beneath the clean optical surface, of fault planes and aberrations that, to a trained eye, told the story of the rock’s past - how it was formed, and what had happened to it in the eons since. She published her results in a series of 1960 papers which laid out crystallographic methods for detecting stacking faults in feldspars, and using structural insights to improve geological modeling. 



Megaw retired in 1972, but like many “retired” scientists kept finding her way back to Cambridge where a desk was kept open for her use. She spent most of her time in her Ballycastle home in Northern Ireland, where she devoted herself to gardening, and to educational efforts to widen access to the exciting insights offered up yearly by crystallographic researchers. She passed away in 2002 at the age of 94, the last of the great first generation of women crystallographers (Franklin died in 1958, Lonsdale in 1971, and Hodgkin in 1994), whose work was never as publicly celebrated as those of her famous colleagues, but the results of whose genius are there at work every time we turn on a computer, record a song, or power up an electric car, and for the woman whose personal measure of the greatness of a piece of research was its practicality and utility, there could have been few legacies so satisfying as that.


FURTHER READING:


One of the last students Megaw worked with, Mike Glazer, wrote down his recollections of her life and methods, which you can find both in Out of the Shadows (2006) and in a slightly different and expanded form in his 2018 appreciation of her for the American Crystallographic Association. Her own classic books, Ferroelectricity in Crystals (1957) and Crystal Structures: A Working Approach (1973) are both well out of print, unfortunately, and if you are looking for a second hand copy it’s going to be something upwards of $100 to flag one down, if there is even one to be had, so best of luck on that!

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