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Tamas Varga

Different Applications of High Pressure as a Tool to Induce Phase Transformations in Solid State Materials. Tamas Varga. Postdoc Brown Bag Seminar December 17, 2008. Photo: http://www.gsecars.org/hp_press_home_files/image009.jpg. Bio. M.S. Chemistry – Debrecen, Hungary (1995)

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Tamas Varga

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  1. Different Applications of High Pressure as a Tool to Induce Phase Transformations in Solid State Materials Tamas Varga Postdoc Brown Bag Seminar December 17, 2008 Photo: http://www.gsecars.org/hp_press_home_files/image009.jpg

  2. Bio • M.S. Chemistry – Debrecen, Hungary (1995) • Ph.D. Chemistry – GA Tech, Atlanta, GA (Prof. Angus Wilkinson) (2005) - Synthesis and structure of low and negative thermal expansion (NTE) materials • Postdoc I. – UC Davis, Prof. Alexandra Navrotsky - Calorimetry of NTE materials and polymer-derived ceramics • Postdoc II. – Argonne, MSD, Dr. John Mitchell - High-pressure synthesis of new materials

  3. Story The Diamond Makers - by Robert M. Hazen, Cambridge University Press, 1999

  4. High-pressure synthesis overcomes reaction barriers New crystal forms, metals, superconductors, etc. New tools/methodology High Pressure (R)Evolution: from diamond making to today’s condensed matter science Pressure Composition Temp

  5. Outline • High-pressure SXRD study of Sc2W3O12 (GA Tech) • Calorimetric study of ZrW2O8 (UC Davis) • High-pressure synthesis of Sc0.67WO4 (ANL) • Weak ferromagnetism and polar order in the HP phase of FeTiO3 (ANL)

  6. Negative thermal expansion materials • NTE: CTE < 0 • Composites (e.g. Cu/ZrW2O8), substrates for matching/control thermal expansion (optical gratings, circuit boards, heat sinks, dental restorations,laser devices) • AM2O7 (e.g. ZrV2O7), AM2O8 (A=Zr,Hf; M=Mo,W) A2M3O12 (e.g. Sc2W3O12) AMO5 (e.g. NbOPO4), MO3-type (e.g. TaO2F) families, zeolites • Mechanism: ZrW2O8 M. A. White: http://myweb.dal.ca/mawhite/Research.htm

  7. Outline • High-pressure SXRD study of Sc2W3O12 (GA Tech) • Calorimetric study of ZrW2O8 (UC Davis) • High-pressure synthesis of Sc0.67WO4 (ANL) • Weak ferromagnetism and polar order in the HP phase of FeTiO3 (ANL)

  8. Compounds with the Sc2W3O12 structure • A2M3O12: M = Mo or W; A = Al – Eu • NTE: A = Al, Cr, Fe, Sc, Y, In and Lu – Ho • orthorhombic structure • anisotropic TE behavior (b expands) • monoclinic on cooling: loss of NTE • NTE involves polytetrahedral tilting • On compression?

  9. In-situ high-pressure SXRD of Sc2W3O12 in a DAC at CHESS • B-2 line at CHESS; HDAC, 0 - 6.6 GPa, isopropanol medium

  10. High-pressure behavior of Sc2W3O12 - SXRD Varga, Wilkinson et al., Phys. Rev. B 71, 214106 (2005) • Ortho.-mono. phase transition observed at 0.3 GPa • Highly anisotropic compressibility in orthorhombic region • Mechanism of volume reduction different from that seen on heating • Unusual decrease in bulk modulus at phase transition

  11. Conclusions on Sc2W3O12 study • Variation of lattice constants on compression and compressibilities determined for the first time • In situ detection of ortho-to-mono transition at low pressure (normal +ve TE) • High and anisotropic compressibility in Sc2W3O12 • Volume reduction more isotropic on P than on T and mechanism is also different

  12. Outline • High-pressure SXRD study of Sc2W3O12 (GA Tech) • Calorimetric study of ZrW2O8 (UC Davis) • High-pressure synthesis of Sc0.67WO4 (ANL) • Weak ferromagnetism and polar order in the HP phase of FeTiO3 (ANL)

  13. PIA in NTE material ZrW2O8 • Pressure-induced amorphization (PIA) observed at relatively low P in several NTE materials • Amorphous phase: metastable intermediate • Interest not purely academic: high P composite processing  TE characteristics • Knowing the relative energetics of crystalline and amorphous phases of materials helps better understand occurrence and mechanism of PIA • Lack of reports of Hf or Gf for ZrW2O8 polymorphs

  14. Entropy increase from amorphous to crystalline? Perottoni et al., Solid State Commun.134, 319 (2005) • Recent study suggests an increase of S in the amorphous to cubic phase transition in ZrW2O8! • Endo recrystallization  vibrational S in cubic phase overrides loss of configurational S

  15. High-pressure synthesis and calorimetry Walker-type HP multianvil press, 7.5 GPa at room T, slow decompression • Solvent: 3Na2O4MoO3 • Temperature: 700 oC Navrotsky, Phys. Chem. Minerals2, 89-104 (1977) Navrotsky, Phys. Chem. Minerals24, 222-241 (1997)

  16. Amorph. material enthalpically less stable than crystalline ones Varga et al., Chem. Mater. 19(3) 468-476, 2007 ZrO2 (solid, 298 K)  ZrO2 (dissolved, 975 K) H1 WO3 (solid, 298 K)  WO3 (dissolved, 975 K)H2 ZrW2O8 (solid, 298 K)  ZrO2 (dissolved, 975 K) + 2WO3 (dissolved, 975 K) H3 ZrO2 (solid, 298 K) + 2WO3 (solid, 298 K)  ZrW2O8 (solid, 298 K) Hf, ox Hf, ox = H1 + 2H2 - H3

  17. Conclusions on stability of ZrW2O8 phases • The pressure-amorphized phase has higher H than the crystalline ones • The exothermic amorphous to crystalline transition suggests that the S of the amorphous phase is greater than that of the crystalline phases (in contrast to previous report) • The amorphous phase can be viewed as a metastable, and may be intermediate, state between the low P crystalline phase and the high P thermodynamic equilibrium product(s)

  18. Outline • High-pressure SXRD study of Sc2W3O12 (GA Tech) • Calorimetric study of ZrW2O8 (UC Davis) • High-pressure synthesis of Sc0.67WO4 (ANL) • Weak ferromagnetism and polar order in the HP phase of FeTiO3 (ANL)

  19. High-pressure transformation of NTE material Sc2W3O12 Sc2(WO4)3 ?? new phase Lattice constants fit wolframite-type MnWO4

  20. Structural and electronic transformation to wolframite Sc2(WO4)3 “ScWO4” Reduction of W, chains of edge-sharing octahedra could explain change in color WO4tetrahedra W(VI) – d0 WO6octahedra W(V) – d1 We have too much Sc!

  21. Electrical properties - semiconductor • Seebeck S<0 • n-type carriers • Metallic thermopower: -15 V/K • Insulator

  22. Crystal structure determination “WO6” • Highly distorted octahedron • W BVS = 6.2 (ortho: 5.8) “ScO6” • Sc site is 2/3 occupied, giving composition Sc0.67WO4 = Sc2W3O12 • Highly defective wolframite-type structure • Slightly distorted octahedron • Sc BVS = 2.4 (ortho: 3.05) 22

  23. Band structure E W 5d • IR: optical bad gap: 0.1 eV • Donor states in W 5d band • Presence of O vacancies E  0.1 eV defect states O 2p N(E)

  24. General picture: ABO4-type materials Scheelite Wolframite Sc0.67WO4 • HP: reversible scheelite  wolframite transformation • Sc0.67WO4 falls in expected range for wolframite type • EuMoO4 – Sleight, 1972; Eu0.67MoO4 - Banks et al., 1974. No A3+WO4 wolframite has been known A. Sleight, Acta Cryst. B28, 2899 (1972) ScO0.95: a = 4.48 Å (V Dudek et al. Monat. Chemie 98, 2424 (1967)

  25. Conclusions on Sc0.67WO4 (High-pressure synthesis, crystal and electronic structures of new scandium tungstate Sc0.67WO4; Varga, Mitchell et al., to be submitted to Chem. Mater.) • New compound, Sc0.67WO4, first wolframite with a 3+ cation • Insulator turns into semiconductor; conductivity due to O vacancies adding electrons to conduction band • NTE materials can serve as precursors to HP synthesis to give new phases (explore different NTE precursors: A2M3O12 family, etc.)

  26. Outline • High-pressure SXRD study of Sc2W3O12 (GA Tech) • Calorimetric study of ZrW2O8 (UC Davis) • High-pressure synthesis of Sc0.67WO4 (ANL) • Weak ferromagnetism and polar order in the HP phase of FeTiO3 (ANL)

  27. Polarization and weak ferromagnetism in MTiO3 Motivation Multiferroics: strong coupling of polarization (FE) and magnetization (FM) MTiO3 (M = Mn, Fe, Ni) promising candidate structures: polar lattice distortion induce weak ferromagnetism (Fennie, PRL, 100, 167203, 2008). Need to make LiNbO3 type phase under high pressure! Ti4+ Fe2+ FeTiO3 R3c Ti4+ Fe2+ Ti4+ Fennie, PRL 100, 167203, 2008 Figure 1

  28. WFM coincident with AF transition

  29. SHG shows polarization • HP phase of FeTiO3 is polar, wile no SHG signal in ilmenite • Next: prove that polar lattice distortion and weak ferromagnetism are coupled (electric field switching of magnetism), need single xtal of HP phase of FeTiO3 (Coexistence of Weak Ferromagnetism and Polar Order in the High-Pressure LiNbO3-type Phase of FeTiO3; Varga et al., to be submitted to PRL) Figure 3

  30. ZrW2O8 Prof. Alexandra Navrotsky Prof. Angus Wilkinson Prof. Cora Lind Dr. Hongwu Xu Prof. Charles Lesher Sc2W3O12 Prof. Angus Wilkinson Prof. Cora Lind Prof. William Bassett Dr. Chang-Sheng Zha Acknowledgments Sc0.67WO4 Dr. John Mitchell Dr. Jun Wang Lindsay Arnold Dr. Brian H. Toby Dr. Christos Malliakas FeTiO3 Dr. John Mitchell Amit Kumar Eftihia Vlahos Dr. Moonkyu Park Dr. Seungbum Hong Dr. Takeshi Sanehira Dr. Yanbin Wang Prof. Craig Fennie Prof. Venkatraman Gopalan Money: NSF DOE-BES Experiments: CHESS APS (ANL) THANK YOU!

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