Research areas
Solid electrolytes
 It was clear to me in the end of the 1970s that high resolution electron microscopy (HREM) would play an important role in future material science and solid state chemistry. I started to use HREM for determination of the defect structure of beta-alumina. These ceramic materials were under intense investigation in test batteries by several international research groups at that time. It was found that the ceramic tubes of beta-alumina caused a short-circuit after a few recharging cycles. In collaboration with scientists at the laboratory of British Railway, studies were started using HREM. I showed that under the influence of the electron beam the ionic conducting layers collapsed because of reduction of the conducting metal ions. For the first time it was published a sequence of images from HREM showing a dynamic event, including a structure transformation. The results were published in Nature and it gave international response. Several groups in USA, Japan and England followed it up and verified the results. Our research on cycled beta-alumina also showed that the same type of defects, with collapsing conducting planes, occurred and most likely caused the short circuit problems.
In 1978 I got an invitation from Professor M. O'Keeffe, the director of the Centre for Solid State Science at the Arizona State University, to work as a research associate there. During my one year stay I worked in the field of solid state ionics, but I also had great opportunities to work with HREM. ASU is the world leading center for microscopy. Almost all internationally well known microscopists have passed this center for HREM. I still have the great privilege to collaborate with scientists there.
My work with Professor O'Keeffe resulted in the discovery of the new fast ionic conductor NaMgF3 and its importance for the understanding of the ionic conduction in the lower mantel of the earth was published in Science.

Structure building principels
 Several new phases in the beta-alumina ceramics were found during the HREM investigations. Using simple structure building principles, like mirrowplanes, on the ccp-based beta-alumina structure, several structures, with unit cells of tenth of nanometer in one direction were determined.
Also in collaboration with Professor O'Keeffe synthetical work was done in order to understand the important structure building principle, chemical twinning. We showed that chemical twinning plays a role in crystallization of compounds belonging to the pinakiolite (M3BO5) family. HREM images revealed that the same crystal could accommodate several structures, belonging to the members of the pinakiolite family, just by changing the chemical twin sequence. From a large number of preparations of synthetical crystals it was shown that these twin sequences are depending on the chemical composition of the crystal. During our work on natural minerals of the pinakiolite family a new mineral, named by us as Takeuchiite, was discovered using the electron microscope. For the first time a crystal structure was deduced from direct structure images and structure building principles known for the same family of minerals. In collaboration with Professor Rolf Norrestam we have shown that the structures of this family contain a disordered row of different transition metals.
The development of analytical electron microscopy now makes it possible to analyses the element content in such small areas as 1 nm in diameter. Using EDS techniques it was later on possible to determine that the concentration of antimony, in the local defects of the crystals of the pinakiolite family, plays an important role for the twin sequence.


Structure determination using single crystal X-ray diffraction and HREM
 I was, in 1987, invited to work as visiting Professor at the Technical University of Denmark. I introduced HREM at the department of Structural Chemistry. During three months, my collaboration with Professor Rolf Norrestam was intensified and we started a systematic structure investigation of the oxyborates. For the first time, single crystal x-ray diffraction and HREM was done on the same crystal. It was shown that even if the x-ray structure determination indicated a perfect average structure of the crystal, the local structure studied by HREM could show plenty of extended planar defects. The same type of structure determinations with x-ray and HREM have been performed for a number of compounds by us and it has been shown that a true crystal structure determination is not complete without a determination of the average structure as well as the local defect structure. It is obvious that also local structural features play an important role for the chemical and physical properties of the crystal.
During the stay in Denmark, studies on phases found in the systems of high-Tc superconductors were carried out. A new La-Cu oxides were discovered and characterized with x-ray and HREM, once again illustrating the complementary use of the two methods since several attempts by other groups have given the wrong answer.

Catalysts
 Research in catalysis has highest priority in most industrial countries today, mostly because it is one important way to save energy in chemical processes. Among the results published in this field, the discovery that some catalysts change their outer surfaces into an amorphous state, can be mentioned. This has been suggested before, but our images showed it for the first time in a used catalyst.
When the big rush around the new superconductors started it was obvious from our point of view that the oxygen pump YBa2Cu3O6+x would be a good candidate for a catalyst for oxidation of organic molecules. We started in the early spring 1987 to study the defect structure of catalytically active modifications of the 1-2-3 compounds and found that indeed all of them showed remarkable properties and the results were published in Nature. We have now patent on the use of 1-2-3 compounds for ammoxidation of aromates.

Structure dynamics
 In the beginning of the 1980s my research group started to use a new HREM microscope with a structure resolution of 0.23 nm. A low-light TV-camera was mounted on the microscope, for direct recording of video sequences at atomic resolution. We started to study small gold clusters (>1nm), made by Professor Schmid's group in the University of Essen, and real time video processing made it possible to reveal new properties of such particles besides their size and structure. The smaller the particles were, the faster their structure was rearranged. We were the first research group to present the dynamic behaviour of small metal particles by showing a video at a cluster congress in Berlin in 1984. The same film also showed how a new atom layer was added to the surface of a gold particle. At the congress, the well known microscopist, S. Iijima, saw this video and he verified our results by showing a videofilm at a congress in Arizona in 1985. We presented at the same congress a new video and the comments by the organizers in a local newspaper mentioned the videos as the highlight of the meeting.
Our pioneering work on clusters started a new research field, now going on in many laboratories in Japan, USA, France and England. Even if we already in 1982 published atomic resolution images of surfaces with the so called surface profile method, we had to find better resolution by collaborating with other research groups. There was a newly installed 400 kV microscope at Arizona State University and we were invited to use it. Many hours of video were recorded and later videoprocessed in our laboratory. For the first time, images of the dynamics of clouds of atoms outside surfaces were obtained. One of my images was presented 1985 on the cover of Nature and the news were commented upon in the same journal by an english physicists. HREM investigations of different metals, done later on, have shown that the clouds exist very commonly outside some surfaces of small metal particles. No satisfactory explanation has been found for the cloud phenomenon, even if several research groups have identified them, even at ultra high vacuum. The clouds also exist as a stage preceding growth of a new surface layer, just before the first atoms coordinate to the surface, in an ordered way. The studies of small metal particles are going on and are also including catalytically active metals like Pt, Pd, Rh, Ru and Ag.
The properties of small metal particles can be summarized as follows:

  1. The total structure can rearrange very fast. Up to four different structure types can be identified in a few seconds.
  2. Clouds of atoms exist outside some surfaces.
  3. Surface growth mechanisms can be followed atom column by atom column.
  4. Surface defects, like rucks, can be identified and their dynamics (surface diffusion) can be followed.
  5. The icosahedral structure found in small particles may well be related to the structure of quasi crystals.

The Royal Academy of Sciences of Sweden gave me the Lindbom award, 1986, for the discovery of the dynamic nature of small particles. In the same year the Swedish Natural Science Research Council (NFR) appointed me a special research position with the motivation: Bovin has with his work documented him to be a world leading scientist in electron microscopy.

The structure of zeolites
 It has been known for a long time that it is possible to implant metallic clusters or molecules inside the cavities of the zeolites by different methods, but only in very few cases, the exact configuration of the cluster or the molecules is known, in conjunction with the network. It is very important to develop methods to study this with HREM. We have worked out structure determination methods for HRTEM studies of confined metals in zeolites.