MIXED-VALENT TRANSITION METAL OXIDES Mas A. Subramanian, Oregon State University, DMR 0804167

1. MIXED-VALENT TRANSITION METAL OXIDESMas A. Subramanian, Oregon State University, DMR 0804167 • This is an exploratory research project on the design, synthesis and characterization of new mixed-valent transition metal oxides with novel functions. The compounds were screened for several properties including multiferroics (dielectric and magnetic properties), superconductivity, thermoelectricity, optical and photocatalysis. • During our exploration of magnetodielectric materials , we discovered the formation of durable intense color pigments (blue, orange, green) based on Y(In,Mn,Cu,Ti,Fe)O3 compositions crystallizing in hexagonal structure with transition metal in trigonal bipyramidal coordination. Recently we have extended this discovery to the other crystal structures such as brownmillerite (A2M2O5). This structure consists of alternate stacking of tetrahedral and octahedral sheets. Highly durable turquoise to green pigments have been designed by substituting Mn5+ in tetrahedral sites of Ba2In2O5(Fig. 1). • Many new compounds with interesting structure and properties were discovered in this program. Recently, a new layered compound Li3Ni2BiO6 with honeycomb ordering between Ni2+ and Bi5+ within the slabs, with Li+ ions in octahedral sites in the inter-slab space (Fig. 2). By topotactic molten salts ionic exchange, a new delafossite compound Ag3Ni2BiO6 has been discovered. The electrochemical lithium ions deintercalation and intercalation is possible which make them potential candidates as cathodes for Li ion batteries (Inorg. Chem., 2012, 51 (9), pp 5377–5385) Fig. 1. Brownmillerite structure (top). Colors of Ba2In2-xMnxO5+xsamples, left to right, x = 0, 0.1, 0.2 and 0.3. (bottom). Mn substitutes as Mn5+ in tetrahedral sites. Fig. 2. A3M2XO6 structure view evidencing the layered organization of Ni2/3Bi1/3O2 slabs (blue and yellow edge-shared octahedra) and LiO2interslab (in grey, only one octahedron is drawn for clarity). (b) honeycomb-type Ni2+/Bi5+ ordering within the slab.

2. MIXED-VALENT TRANSITION METAL OXIDESMas A. Subramanian, Oregon State University, DMR 0804167 • Broader Impact: A patent application by OSU covering the color pigment compositions has been granted by US patent office. Recently, Shepherd Color Company have shown these pigment have high reflectivity in near IR region (high solar heat reflectance) and can be potentially used in 'cool roofing’ applications for ‘greener’ buildings design and other related applications such as automotive paints. This has drawn increased attention from several international pigment/paint manufacturers such as Merck, BASF, PPG. • Education and Outreach: This program is providing training for both undergraduate and graduate students in synthetic materials chemistry, crystal structure analysis and electronic properties. This program also provides these students with the intellectual challenge of understanding the complex behavior of newly synthesized materials and help forge links between chemistry, physics and material science. Students participating in this research program is gaining experience that will prepare them well for the academic and modern industrial environments A demonstration kit showing various color pigments (pictured right) has been developed for actives involving high school students, artists and for general public education regarding the importance of discovery research and how it impacts society. Our pigment discovery is widely used in undergraduate teaching and projects in many US universities and abroad. . Pigment Demonstration Kit Four undergraduate students participated in this program in 2011-12; Casey Young (top left, microwave synthesis of pigments), Matthew Stolt (bottom left, photocatalyst synthesis), Jeffrey Porter (top right, red pigments) and Omar Rachdi (bottom right, dielectrics).