Intraatomic vs Interatomic Interactions John B. Goodenough (University of Texas at Austin) DMR Intellectual Merit Localized electrons have stronger intraatomic interactions, itinerant electrons have stronger interatomic interactions. Presently we are monitoring the evolution of structural and electronic properties at the crossover from localized to itinerant electronic behavior in AMO 3 perovskites in which only the π-bonding orbitals of the transition-metal M-cation d orbitals are occupied. The orthorhombic RVO 3 perovskites (R = rare earth) have two localized π-bonding 3d electrons per V 3+ ion, and a threefold orbital degeneracy in a cubic site leaves an orbital angular momentum L to give an intraatomic spin- orbit coupling L  S to compete with the interatomic spin-spin S i  S j interactions responsible for magnetic order below a T N. We have previously shown that a local VO 6/2 -site distortion accompanies orthorhombic crystal symmetry to bias an orbital ordering below a T OO > T N that suppresses L for R = Pr  Lu. We show here that in LaVO 3 where T N ≈ T OO, an interatomic spin-spin frustrated by competition from (L  S) coupling is resolved by the orbital ordering.

Intraatomic vs Interatomic Interactions John B. Goodenough (University of Texas at Austin) DMR Broader Impact Our use of high pressure as a variable for studying the evolution of physical properties at the crossover from localized to itinerant electronic behavior has resulted in collaboration with the Institute of Physics, Chinese Academy of Science in Beijing, China, and with the Institute for the Study of the Earth’s Interior, Okayama University in Japan. We illustrate with a figure from a collaborative paper, C.-Q. Jin, J.-S. Zhou, J.B. Goodenough, Q.Q. Liu, J.G. Zhao, L.X. Yang, Y. Yu, R.C. Yu, T. Katsura, A. Shatskiy, and E. Ito, Proc. Nat. Acad. Sci. 105, 7115 (2008). Our synthesis of BaRuO 3 has interested the geoscientists as it represents a phase that can exist under the pressure of the Earth’s interior. Sr 1-x Ba x RuO 3 is an itinerant-electron ferromagnet. In Sr 1- x Ca x RuO 3, breaking of spin-spin interactions between Ru neighboring Ca is responsible for the Griffiths phase. Phase diagram of the magnetic transition temperatures versus the tabulated average A-site ionic radius 〈 r A 〉 for Sr 1-y Ba y RuO 3 and Sr 1- x Ca x RuO 3

Notes The evolution of electronic and structural properties at the crossover from localized to itinerant electronic behavior continues to reveal surprises. In oxides, the occupied d orbitals of an octahedral-site transition-metal ion lie in the energy gap between empty and filled s and p bands of the cations and anions, respectively. In an AMO 3 perovskite, the strength of the interatomic M  O  M interactions vis à vis the intraatomic interactions on a transition-metal M cation determine whether the 3d electrons remain localized or are transformed into itinerant electrons occupying one-electron band states. Cubic crystalline fields at an MO 6/2 site split the fivefold-degenerate d orbitals into a threefold-degenerate set of t orbitals that π-bond with the bridging oxygen and a higher energy twofold-degenerate set of e orbitals that  -bond with the bridging oxygen. This splitting does not completely quench the orbital angular momentum of a t n e 0 configuration that is orbitally threefold-degenerate (i.e. n = 1,2; 5,6). The strength of the M  O  M π-bond interactions depends on the amount of O  2p wavefunction covalently admixed into the ligand-field t orbitals; as the covalent mixing increases, there is a transition from localized to itinerant electronic character. Since the O  2p orbitals that π-bond with the M  cation t orbitals  -bond with the A cations, the strength of the π-bond interactions can be modulated in an isoelectronic MO 3 array by the acidity and size of the A-site counter cation. Therefore, the perovskite structure allows modulating the strength of the M  O  M interactions of π-bonding electrons by substitution of isovalent A-site cations, as also does the application of hydrostatic pressure. It is this situation that underlies the experimental strategies on the RTiO and RVO 3 perovskites (R = rare earth) and on the ACrO 3 and ARuO 3 perovskites (A = alkaline earth) that we are studying. Reported here are experiments on LaVO 3 where the V 3+ : t 2 e 0 configuration is localized. Note particularly how the thermal conductivity  (T) is low (Figure shows  - 1 (T)) in the paramagnetic phase due to the orbital fluctuations associated with spin-orbit coupling whereas  (T) rises (  -1 (T) falls) sharply below T N and climbs to the phonon values of LaGaO 3 below 100 K. We have also been studying the isoelectronic system Sr 1-x Ca x CrO 3 where the t 2 configuration is transformed to itinerant electrons in a π * band of t-orbital parentage; it exhibits a transition from an enhanced Pauli paramagnetism in SrCrO 3 to itinerant-electron antiferromagnetism in CaCrO 3. We have been collaborating with the Chinese and Japanese on the Sr 1-x Ca x CrO 3 and the Sr 1-x Ba x RuO 3 systems that are prepared under high pressure. See attached figure for the structure of the AMO 3 perovskites. John B. Goodenough (University of Texas at Austin) DMR

Ideal cubic AMO 3 Perovskite Structure Cooperative rotations of the MO 6/2 octahedra about the [001] axis give tetragonal symmetrys about the [i10] axis give orthorhombic symmetry. A M John B. Goodenough (University of Texas at Austin) DMR