Mohammad Yousuf

Mohammad Yousuf

Summary of the most Significant Work

I have made appealing contributions in the area of condensed matter physics, highlighting various types of phase transitions occurring under pressure. In quasicrystalline Al-Fe, I showed an isostructural electronic transition at about 6 GPa and explained the fine structure in electrical resistivity variation with pressure arising due to the devil's stairs case type of electronic structure of quasicrystal. I demonstrated convincingly the reversible crystal−amorphous−crystal transition in tetracyanoethylene compounds. Most noteworthy of my contribution is the unambiguous exposition of crystal structure transformation in binary actinide alloys UAl2 and ThAl2 and technologically potential Ti3Al intermetallic. The crystallography and transition pressures as well as the conclusive evidences for f−electron delocalization have been a commendable feature of my research work. For carrying out these excellent research work, I have painstakingly built novel apparatus necessary for the studies including a Diamond Anvil Cell. I have provided the recipe for improving the ductility in Ti3Al, a potential material for aerospace engineering. I have solved the crystal structures of the gas hydrate samples mined from various geographic locations across the globe. My investigations on the nanomaterials have led to understanding the mechanisms responsible for the formation and stability of nanomaterials. My efforts on the study of Transparent Conducting Oxide have shown that synthesis of a suitable combination of multi-component oxides can make the film chemically and structurally stable at elevated temperatures.


Impact of Contributions on Basic & Applied Research


I have painstakingly built a High Pressure Laboratory, with capability for simultaneous high temperature. I have been instrumental in developing the diamond anvil cell. The concept of Guinier Geometry with diamond anvil cell, rotating anode X-ray generator and Diffractometer is unique. These developmental activities of mine have stimulated high pressure research and have encouraged many research groups to borrow these ideas and benefit from there. Similarly, the success on imaging plate has created interest in researchers in various disciplines. My basic research contribution spans the area of electronic and structural transitions in several novel materials. Particular reference may be made to the significant contribution to actinide-based systems like UAl2 and ThAl2. In recognition of the impact of the work carried out by me, I was invited by the Academic Press to write a review article on the Diamond Anvil Cell in the High Pressure Studies of Semiconductors. The article has appeared in the Semiconductors and Semimetals Vol. 55. The Elettra Sincrotrone has invited me to build a beamline for carrying out the diamond anvil cell based experiments. JCPDS provides the standards for powder diffraction files. Our laboratory has been chosen by the editors to publish our data on f electron systems at STP and at high pressures. AIRAPT International Conference on High Pressure Science & Technology is an international forum where the most recent work on high pressure is presented. The Organising Committees of the AIRAPT-17 and the AIRAPT-18 invited me to act as a member of the International Advisory Committee, to chair technical sessions and give invited talks.


Significant Contributions to Science & Technology



1. I have concentrated on the study of Clathrate Hydrates of Natural Gases. Using the Synchrotron Radiation Source (Advanced Photon Source) at the Argonne National Laboratory, I have solved the crystal structures of the gas hydrate samples mined from various geographic locations across the globe. This investigation is of paramount technological importance in that we could correlate the structural differences in terms of the type and the quantities of natural gases contained in the gas hydrates present at geographically distinct seafloors. 

2. I have focused on the nanomaterials such as quantum dots, nanowires, nanotubes and nanorods. My investigations have led to understanding the mechanisms responsible for the formation and stability of nano-materials. 

3. I have dedicated my efforts on the study of Transparent Conducting Oxide. The interest on TCO emanates from its appropriateness of application in a wide-ranging cutting edge of technology. In a variety of applications, it is required that the TCO films be chemically and structurally stable at elevated temperatures. In our studies, we have shown that synthesis of a suitable combination of multi-component oxides can make the film chemically and structurally stable at elevated temperatures. 

4. I have specialized in the area of high pressure research and I have made outstanding contributions to the science and technology since 1977. I am responsible for setting up a novel high pressure−high temperature electrical resistivity apparatus capable of sustaining 10 GPa and 1000 K simultaneously. I have also set up associated automated resistivity measuring apparatus. Subsequently, I set up the high pressure X-ray diffraction system in angle dispersive and energy dispersive modes. Using this apparatus, I solved the crystal structures at high pressure and obtained the exact amorphous−crystalline transition pressure in selenium. 

5. One of my most striking contributions is the concept of adopting the truly focusing type geometry, namely, the Guinier geometry for the X-ray diffraction system, with the diamond anvil cell, since this geometry offers a truly monochromatic and focused diffracted X-ray beam. For realizing the idea, I developed and set up the required instrumentation consisting of a powerful 18 kW rotating anode X-ray generator, a long body megabar diamond anvil cell (DAC), the Guinier diffractometer with sample in a DAC and the X-ray detector on the Seeman−Bohlin circle. I have used this unique apparatus to solve the crystal structure of several novel materials. For example, I solved the crystal structure of the high-pressure phase of UAl2, which, incidentally, eluded experimenters even with synchrotron radiation source. My very recent studies on ThAl2 system show the existence of a pressure induced structural sequence. I explained this structural sequence using the Villars' 3–parameter structural stability map. Further, I have evolved a new focal theme for our high-pressure research wherein the behavior of f electron based binary compounds is being investigated at IGCAR, Kalpakkam.

6. Ti3Al is an intermetallic compound with a potential of application in aerospace engineering. However, it exists in DO19 structure type and is brittle in nature. In order to get the clue for the alloying element that can stabilize a ductile cubic crystal structure, high pressure experiments were performed. Major finding was that the system undergoes a transition at ~16 GPa from DO19, with no cubic environment to DO24 structure type, having almost 50% cubic environment. I conjectured that it should exhibit a pressure induced structural sequence, before stabilizing into a cubic phase. Synchrotron Radiation Source based experiments have been performed to 1.3 megabar and Ti3Al has been found to stabilize into L12 cubic structure type. 

7. I have elucidated the dominant conduction mechanism in uranium and thorium. I showed unambiguously that spin fluctuation, and not the inter-band electron-phonon scattering, is the main operative mechanism. 

8. I provided a clear evidence for change in Fermi surface and demonstrated a universal behavior under pressure across the magnetic transition in Ni. This work was recognized by The Indian Physical Society by award of the Young Physicist of the year 1986. 

9. For the first time, I demonstrated the pressure induced amorphisation reaction in the system, tetracyanoethylene. I have shown the observation of a structural sequence, namely, Monoclinic−Amorphous−Cubic transition with increase of pressure, and obtained useful kinetics information on the transformation. 

10. I have carried out a series of experiments on quasicrystals such as AlFe, AlMn, and AlFeCu, under high pressure, using the techniques of electrical resistivity and synchrotron radiation source based X-ray diffraction. In the case of AlFe, my important contribution is in demonstrating the existence of an isostructural electronic transition at about 6 GPa. And the fine structure in resistivity data has been ascribed to the presence of devil’s staircase structure in the electronic structure of the quasicrystal

11. I have contributed to the solution of the crystal structure of fullerene C70 at NTP and have examined its pressure-induced behavior. 

12. Apart from the high-pressure studies, I have designed and developed the diamond anvil cell, capable of generating a megabar pressure. This indigenizing effort has culminated into the device, which more than a dozen laboratories in India and abroad are using. 

13. Imaging plate system is the modern X-ray area detector having far superior response compared to the other area detectors. I have successfully developed this system. Engineering modifications have been incorporated to improve the performance. BaFBr: Eu2+ is used as X-ray storage phosphors. I have contributed to the understanding of the basic mechanism of photostimulated luminescence in this material. The question of charge state of Eu in BaFBr matrix has been taken up and found to be 2+.

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