In 1912, Max von Laue, Walter Friedrich, and Paul Knipping performed their famous X-ray diffraction experiment and proved for the first time two basic principles in physics: that a single crystal is composed of regular blocks and that X-rays behave as waves with a wavelength in the order of the distances between the building blocks of the crystal. It is interesting to note, that Fridrich and Knipping also carried out first powder X-ray diffraction experiment. They ground a copper sulphate crystal and placed the powder sample in the X-ray beam instead of a single-crystal. They observed small speckles around a central spot. Unfortunately, they used a polychromatic beam and the exposure was too short to observe diffraction rings [1].
The powder X-ray diffraction method was developed independently by Peter Debye and Paul Scherrer (1916) and by Alfred Hull (1917). Debye and Scherer made a 57 mm diameter cylindrical camera, used two films with each forming two half of circle in contact with a camera wall, a primary beam collimator and a light-tight cover. For the sample, they used the finest grain powder of LiF [2]. Debye and Scherrer were surprised to find on the first photographs the sharp lines of first powder diagram, which they correctly interpreted as crystalline diffraction by the randomly oriented micro-crystal of the powder [3]. Approximately at the same time, Alfred Wallace Hull, an employee of General Electric Research Laboratory in USA, became interested in the X-ray diffraction. Hull saw there a challenge and try to find the crystal structure of iron. Since the single-crystals of iron were not available at that time, he used iron fillings, which were rotated continuously in order to provide randomness [3]. He obtained good diffraction patterns and subsequently checked if the d-spacings of the diffraction patterns of iron are consistent to the Bragg values for the three cubic crystal systems [1]. Hull also described many of the experimental factors; was first who used a Kβ filter and measured the effect of X-ray voltage on the intensity of the MoKα radiation. He described the importance of the particle size in the sample, specimen rotation and the necessity for the random orientation. Debye and Scherrer did not mention the use of the method for phase identification in the paper (1916), however Hull recognized that powder diffraction analysis can be used for phase identification of crystalline compounds, even if they are in mixtures. A major advance of the powder diffraction method began in the early 1950´s with the introduction of the first commercial high-resolution diffractometers which greatly expand the use of the method [3]. In 1967, a next huge step was taken as Hugo Rietveld published his first whole profile pattern fitting analysis of WO3 [4]. In this work, Hugo Rietveld showed that he could refine a crystal structure having powder diffraction pattern with overlapping reflections. He also introduced residual values (R factors), allowing the quantitative judgment of the refinement quality.
This contribution illustrates the discovery of powder diffraction in 1916 and further development of the method till the advent of „Rietveld method“ in 1967. The progress in development of instrumentation (including neutron diffraction), powder diffraction databases, and determination of first non-cubic crystal structures will be discussed.