Squeezing Simple Molecules to Novel Conducting Polymers

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TECHNICAL SUMMARY: At sufficiently high pressures, all molecules are expected to transform into metallic extended solids that can, arguably, be considered either elemental metals or metallic alloys. Made of low Z elements such as H, C, N, and O, these extended solids constitute a new class of highly conductive organic polymers or molecular alloys that can exhibit metallic conductivities and novel electronic and chemical properties. We propose a systematic study of pressure-induced transformations of highly covalent Group IV, V, and VI elemental molecules such as C, N2, CO2, and their chemical analogs to novel extended solids of (A) metallic and superconducting states, (B) charge/spin-ordered states, and (C) low-dimensional metallic states. The proposed study will use integrated experimental capabilities to probe crystalline structures (synchrotron x-ray diffraction), electronic structures (inelastic x-ray Raman spectroscopy and optical reflectivity), electrical transport properties (four-probe resistance and susceptibility), as well as phase transitions and bonding (Raman and IR spectroscopy), at Mbar pressures (1 Mbar ~ 100 GPa = 106 atmospheres). The proposed research, supported by the Solid State and Materials Chemistry Program will establish a new periodic perspective on low Z molecular solids at the most fundamental level of elemental alloys. In doing so we will explore several key scientific challenges of extended solids under extreme conditions: (i) the relationships between structural orders (or disorders) and electronic structures, (ii) the charge and spin ordering processes near molecular insulator-to-metal transitions, (iii) the nature of internal pressures in low-dimensional and/or incommensurate structures, and (iv) the differences (or similarities) between low Z covalent polymers and high Z metallic alloys. Addressing these challenges is not only important in understanding the relationships of crystalline structures, electron correlation, and functional properties, but will also have strong implications for novel materials and technology developments at ambient conditions.NON TECHNICAL SUMMARY: The present study will impact broad scientific disciplines including condensed matter physics, solid-state chemistry, and materials and planetary sciences. It will yield new and unexpected discoveries and help establish new periodic systematics of low Z elemental solids at extreme pressures. The study will also help develop a new class of highly conducting metallic and superconducting polymers at ambient conditions, utilizing the concept of chemical alloys and internal pressures. The study will augment and enhance collaborations with national laboratories, synchrotron x-ray facilities, and other academic institutes. Hence, the benefits will reach well beyond the immediate scope of the present proposal. We will train graduate students, undergraduates and post-doctoral fellows, providing significant hands-on opportunities to learn cutting-edge experimental technologies. The present work will provide them with critical tools needed for career development and carrying out independent research. Finally, the proposed study will produce a variety of real-time images and movies showing the beauty of crystal facets and elemental solids and revealing nature's fascinating structural and morphological transformations. These will have many uses, among them, stimulating the scientific imagination and excitement of both K-12 and undergraduate students in this fundamental physical science research.