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        Low temperature synthesis of (noncentrosymmetric) oxide-fluorides
»ã±¨ÄÚÈݼò½é£ºThe design and discovery of novel noncentrosymmetric materials – materials that lack an inversion center – with large second-order dielectric responses, χ(2), that efficiently achieve frequency conversion has been a long-standing and difficult goal of inorganic chemistry. Recently, nanolithography has sought UV lasers to create increasingly small lithographic features. To pursue UV lasers, scientists have sought new SHG active crystals to double the frequency of laser light to higher energies. One such material is the oxide-fluoride KBe2BO3F2. Professor Chen’s Anionic Group Theory has established that efficient SHG-active crystals often have anions with aligned polar moments in the solid state. Therefore, to synthesize highly-efficient SHG crystals, a promising strategy is to utilize anions that inherently contain polar moments. For this reason, our group has examined oxide-fluoride early transition materials; the d0 early transition metal cations undergo out-of-center distortions owing to electronic effects (specifically Second-Order Jahn-Teller distortions). These polar distortions are observed in oxide-fluoride anions of the cations vanadium (V5+), niobium (Nb5+), tantalum (Ta5+), molybdenum (Mo6+) and tungsten (W6+). In oxide phases of these metals, the Second-Order Jahn-Teller distortion is directed towards oxide ligand(s) of corner, edge, or face(s) of the anionic octahedra. The use of oxide-fluoride compounds enhances the distortion of the anion as the metal-fluoride bonds contain less valence than would exist for metal-oxide bond. The additional valence thus creates stronger M=O bonds within the anions of the solid state compound and thus a stronger distortion. Our syntheses of numerous inorganic and organic-inorganic hybrid oxide-fluoride phases have allowed the analysis of the electronic environments of the early transition metal polyhedra; the distortions of the anions and non-spherical electronic environments have allowed us to synthesize non-centrosymmetric materials and establish principles and guidelines to target syntheses of SHG-active materials.

 

»ã±¨ÈËÐÕÃû£ºKenneth R. Poeppelmeier

 

»ã±¨È˼ò½é£ºKenneth R. Poeppelmeier ÃÀ¹úÎ÷±±´óѧ½ÌÊÚ ÃÀ¹úÎ÷±±´óѧ´ß»¯Óë±í±í¿ÆѧÖÐÐÄÖ÷ÈÎ ÃÀ¹úÎ÷±±´óѧ³¬µ¼¿ÆѧÓë¼¼ÊõÖÐÐĸ±Ö÷ÈÎ ÃÀ¹ú»¯Ñ§»á“ÎÞ»ú»¯Ñ§”¸±Ö÷±à ÃÀ¹ú»¯Ñ§»áÎÞ»ú»¯Ñ§Óë¹Ì̬»¯Ñ§·Ö»áÖ÷ϯ ÃÀ¹ú“ºÏ½ðÓ뻯ºÏÎï”±àί
»ã±¨È˼ò½é(Ó¢ÎÄ)£ºKenneth R. Poeppelmeier Charles E. & Emma H. Morrison Professor of Chemistry Director of Center for Catalysis and Surface Science Associate Director, Northwestern University Science and Technology Center for Superconductivity Associate Editor, Inorganic Chemistry Chair, American Chemical Society Division of Inorganic Chemistry & Solid-State Chemistry Editorial Boards, Journal of Alloys and Compounds,
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     Center for Catalysis and Surface Science£¬Northwestern University, USA
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