MAUGUIN, CHARLES VICTOR

(b. Provins, France, 19 September 1878; d. Paris, France, 25 April 1958)

crystallography, mineralogy.

Mauguin was the son of a baker in Provins, a small city fifty miles southeast of Paris. He attended primary school in Provins and, from 1894 to 1897, the École Primaire of Melun, in order to become a teacher. He began his university career in Montereau, where he also taught at the elementary school, while preparing for the entrance examination for the École Normale of Saint-Cloud, which he attended from 1902 to 1904. At this school, established to train teachers for the écoles normales primaires, students received thorough instruction in mathematics, physics, chemistry, and the natural sciences. A brilliant student, Mauguin attracted the attention of L. J. Simon, who suggested that he work in his organic chemistry laboratory at the École Normale Supérieure in Paris. In 1910 Mauguin defended his doctoral thesis, “Les amides bromées-sodées et leur rôle dans la transposition d’Hofmann.”

At the Sorbonne, Mauguin took the mathematics courses of Émile Picard, Poincareé, and Goursat and attented the lectures given there in 1905 by Pierre Curie on symmetry in physical phenomena—his first contact with crystallography. He then attentded the courses of Frédéric Wallerant, the professor of mineralogy and crystallography. The lattger was interested in liquid crystals, which had been discovered a few years previously by the German physicist Otto Lehmann. These organic substances, in a well-defined temperature interval between the liquid and the solid phase, present a curious state of matter that is characterized by the great fluidity of liquids and optical properties similar to those of crystals.

Attracted by crystallography 1910 Mauguin became Wallerant’s assistant in the mineralogy laboratory of the Sorbonne in order to study liquid crystals. His memoirs on this subject published from 1910 to 1914 are fundamental to an understanding of the liquid-crystal state. He was named lecturer in mineralogy at the Faculty of Sciences of Bordeaux in 1912 and professor of mineralogy at the Faculty of Sciences of Nancy in 1913. He was mobilized in the infantry upon the declaration of war and later worked in a chemistry laboratory. At the end of 1919 he returned to the Sorbonne as a lecturer and in 1933 succeeded Wallerant in the chair of mineralogy, which he occupied until his retirement in 1948. All of his researches were concerned essentially with the diffraction of X rays by crystals.

Mauguin’s marriage in 1907 to Louise Gaudebert was childless. Mme Mauguin became blind in 1930; and from then on, they led a retiring life and died within a few months of one another. Until the end of his life, Mauguin preserved an intellectual and youthful enthusiasm for science; his whole life was devoted to studies of extremely varied questions. Long interested in mathematics, especially group theory and Laplace-Fourier transforms, he later turned his interest to theoretical physics and in his last years paid special attention to biological work dealing with the genesis of life. He was a remarkable teacher who could clarify the most difficult questions. His great pleasure, before his wife’s illness, was to go on excursions in the mountains and woods to search for plants; he was an excellent botanist and was president of the Mycological Society of France. He was also laureate of the Institut de France in 1922 and in 1928. In 1937 he was elected a member of the Académie des Sciences.

Mauguin’s first researches in organic chemistry dealt with the amides RCONH₂, in which he replaced the two hydrogen atoms with one atom of bromine and of sodium; the liberation of NaBr furnished isocynates O.CN.R. He thus established a close link between the amides and the ureides, which play a role of great importance in the chemistry of living cell. Throughout his life Mauguin was interested in the biological aspect of chemistry.

In the temperature region that characterizes the liquid-crystal state, the liquid crystal appears in the form of a turbid liquid, almost opaque when in a thick layer. Some scientists explained this cloudiness by the presence of an insoluble impurity. Mauguin showed that the liquid is made up of birefringent elements in random orientation so that it loses its transparency. Azoxyanisole and azoxyphenetole, which in the turbid phase are extremely fluid, become homogeneous and perfectly transparent when a uniform orientation is imposed on the birefringent elements, either by the action of a magnetic field or by suitable surface actions.

Placed between the poles of an electromagnet, the liquid-crystal phase behaves, optically, like strongly birefringent uniaxial crystal with optical axis parallel to the magnetic field. Mauguin made a complete optical study of this phenomenon, measured the indices of refraction, and reproduced all the classic experiments of optical crystallography.

Similarly, when melted between two completely clean glass plates, azoxyanisole yields a transparent homogeneous phase and behaves like a uniaxial crystal with optical axis perpendicular to the surface. If azoxyanisole is melted on a freshly cleaved flake of muscovite, the optical axis is parallel to the cleavage plane (001) in a direction (100) 30° from the plane of symmetry (010); this fact, unexpected at the time (1912), was explained by Mauguin after X rays showed that the plane of symmetry of mica is a plane of glide symmetry. If the melting takes place between the two surfaces of a cleavage, the two optical axes in contact with the two flakes from an angle of 60°; the result is a helicoidal structure, of which Mauguin made a detailed theoretical and experimental study. These results, established with remarkable rigor and clarity, excited great interest and are still valuable.

Upon returning to the laboratory after World War I, Mauguin, impressed with the importance for crystallography of the discoveries of Laue and the Braggs, devoted himself completely to X-ray crystallographic studies. In 1923 he published the atomic structure of cinnabar, followed by those of calomel and graphite. He next undertook long crystal-chemical researches on the micas and the chlorites, among which the unity of crystallographic properties is in contrast with the variety of chemical compositions. Mauguin determined the chemical composition of a great number of micas; their density; and, by means of X rays, the absolute values of their cell dimensions. He was thus able to determine the number of atoms contained in the unit cell. He established that the crystal motif for all the micas always includes twelve oxygen and fluorine atoms, although the number of cations varies within large limits and can be fractional, proving that the simple motif is not always repeated identically in the crystal (Bulletin de la société française de minéralogie, 51 [1928], 285–332). In the chlorites the crystal motif always has eighteen oxygen atoms.

Mauguin worked a great deal on group theory; his memoir of 1931 represented the 230 Schönflies-Federov groups by simple symbols, describing the symmetry elements precisely and expressing directly the symmetry operations determined by X-ray diffraction. These symbols, slightly modified following a collaborative effort with C. Hermann, are universally employed and have made Mauguin’s name familiar to crystallographers.

BIBLIOGRAPHY

The papers by Mauguin referred to in the text are “Étude des micas au moyen des rayons x,” in Bulletin de la Socīété française de minéralogie, 51 (1928), 285–332; “La maille cristalline des chlorites,” ibid., 53 , (1930), 279–300; and “Sur le symbolisme des groupes de répétition ou de symétrie des assemblages cristallins,” in Zeitschrift für Krystallographie, 79 (1931), 542–558.

On Mauguin and his work see P. P. Ewald, Fifty Years of X-Ray Diffraction (Utrecht, 1962), pp. 335–340; and J. Wyart, “Ch. Mauguin 1878–1958,” in Bulletin de la Société française de minéralogie et de cristallographie, 81 (1958), 171–172.

Jean Wyart