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MAGNETIC GARNETS, Y x Gd 3-x Fe 5 O 12 TUNABLE MAGNETIC GARNETS

MAGNETIC GARNETS, Y x Gd 3-x Fe 5 O 12 TUNABLE MAGNETIC GARNETS. Y(NO 3 ) 3 + Gd(NO 3 ) 3 + FeCl 3 + NaOH  Y x Gd 3-x Fe 5 O 12 Mixed metal hydroxide aqueous precursor synthesis method, reactants red brown, solid products olive green

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MAGNETIC GARNETS, Y x Gd 3-x Fe 5 O 12 TUNABLE MAGNETIC GARNETS

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  1. MAGNETIC GARNETS, YxGd3-xFe5O12TUNABLE MAGNETIC GARNETS • Y(NO3)3 + Gd(NO3)3 + FeCl3 + NaOH YxGd3-xFe5O12 • Mixed metal hydroxide aqueous precursor synthesis method, reactants red brown, solid products olive green • Firing pellets at 900oC, 18-24 hrs, re-grinding, re-pelletizing, repeated firing, removes REFeO3 Perovskite impurity • PXRD used to identify garnet phase, detects any crystalline impurity phase like REFeO3, enablesUC dimensions to be determined as a function of Y: Ga ratio over range 0 < x < 3

  2. PXRD OF SOLID PRODUCTS OF Y(NO3)3 + Gd(NO3)3 + FeCl3 + NaOH REACTION

  3. aqueous basic medium, mineralizes, temperature gradient transports, deposits reactants on seed crystal to grow product yttrium gadolinium iron oxide crystal baffles T2 T1 T2 Gd2O3 /Y2O3 Fe2O3 Seed crystal to grow YxGd3-xFe5O12 crystal HYDROTHERMAL SYNTHESIS AND CRYSTAL GROWTH OF YTTRIUM GADOLINIUM IRON GARNET

  4. GARNETS DISPLAY INTERESTING COOPERATIVE MAGNETIC BEHAVIOR • Tunable Garnet magnet by varying magnetic sub-lattice components without disrupting garnet structure • Similar idea to magnetic Spinel AB2O4 solid solution behavior - in which one has magnetically tunable Td (A) and Oh (B) metal sites • Rare earth garnets R3Fe5O12 • General Formula C3A2D3O12 (8 formula units per cubic unit cell - total 160 atoms)

  5. ONE OCTANT OF CUBIC UNIT CELL OF Y3Al5O12 (YAG) Faces 3 dodecahedral Y(3+) sites Corners and center 2Oh AlO6 sites Faces 3Td AlO4 sites One octant of cubic unit cell of garnet

  6. YxGd3-xFe5O12 GARNETS DISPLAY INTERESTING COOPERATIVE MAGNETIC BEHAVIOR • C3A2D3O12isomorphous replacement of Y(3+) for Gd(3+) on dodecahedral C cation sites (works for all rare earths except La, Ce, Pr, Nd) • Forms solid solution as similar ionic radii • R(Gd(3+)) = 0.938Å > R(Y(3+)) = 0.900Å • Complete family accessible, YxGd3-xFe5O12, 0  x  3 • 2Fe(3+) Oh A-sites, 3Fe(3+) D Td sites, 3RE(3+) C dodecahedral sites

  7. FACING THE CHALLENGE MODELS FOR DETERMINING THE Y(3+)/Gd(3+) DISTRIBUTION IN YxGd3-xFe5O12 1. Solid solution - random distribution of two components - EDX mapping 2. Physical mixture of two end members - phase segregation - PXRD 3. Compositional gradients - STEM imaging - EDX mapping 4. Core-corona - cherry model - surface free energy driven - EDX mapping 5. Microphase separated domains smaller than 10 nm - PXRD line broadening often to disappearence 6. Ordered superlattice of two components - ED

  8. MODELS FOR DETERMINING THE Y(3+)/Gd(3+) DISTRIBUTION IN YxGd3-xFe5O12 • Interesting problem in solid state materials characterization • If any measured physical property P of the product follows linear Vegard law behavior this defines a solid solution for the Y(3+)/Gd(3+) distribution • P(YxGd3-xFe5O12) = Px/3(Y3Fe5O12) + P(3-x)/3(Gd3Fe5O12) • Measured P of product is the atomic/mole fraction weighted averageP of the end-member materials

  9. MAGNETIC GARNETS, YxGd3-xFe5O12TUNABLE MAGNETIC MATERIALS • Cubic unit cell parameter a versus x for YxGd3-xFe5O12 • CompositionLattice parameter, nm • Y3Fe5O12 1.2370 • Y2.5Gd0.5Fe5O12 1.2382 • Y2Gd1Fe5O12 1.2402 • Y1.5Gd1.5Fe5O12 1.2423 • Y1Gd2Fe5O12 1.2437 • Y0.5Gd2.5Fe5O12 1.2450 • Gd3Fe5O12 1.2468 R(Gd(3+)) = 0.938Å > R(Y(3+)) = 0.900Å

  10. MAGNETIC GARNETS, YxGd3-xFe5O12TUNABLE MAGNETIC MATERIALS • Isomorphous random replacement of Y3+ for Gd3+on dodecahedral sites of cubic lattice • Linear Vegard law behavior • P(YxGd3-xFe5O12) = Px/3(Y3Fe5O12) + P(3-x)/3(Gd3Fe5O12) • Any property of a solid-solution member is the atom/mole fraction weighted average of the end-members - distinguishes statistical from other types of mixtures (core-corona, phase separation, domains, gradients, superlattices) • Cubic lattice parameter a shows linear Vegard law behavior with x

  11. TUNABLE MAGNETIC PROPERTIES BY VARYING x IN THE BINARY GARNET YxGd3-xFe5O12 • Counting e and unpaired e-spins – book keeping • x dodec Y(3+) sites 4d0, 4f0 0 UPEs • (3-x) dodec Gd(3+) sites HS 4f7 7 UPEs • 3 Td Fe(3+) sites HS 3d5 5 UPEs • 2 Oh Fe(3+) sites HS 3d5 5UPEs

  12. TUNABLE MAGNETIC PROPERTIES BY VARYING x IN THE BINARY GARNET YxGd3-xFe5O12 • Ferrimagnetically coupled material, oppositely aligned electron spins on Td and Oh Fe(3+) magnetic sub-lattices • Counting spins Y3Fe5O12 ferrimagnetic at low T • 3 x 5 - 2 x 5 = 5UPEs • Counting spins Gd3Fe5O12 ferrimagnetic at low T • 3 x 7 -3 x 5 + 2 x 5 = 16UPEs • Tunable magnetic garnet: 16 to 5 UPEs

  13. VEGARD LAW AT THE NANOSCALE SYNTHESIS OF COMPOSITION TUNABLE MONODISPERSE CAPPED ZnxCd1-xSe ALLOY NANOCRYSTALS

  14. SYNTHESIS OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS • Sequential synthesis of small Eg core and large Eg shell precursor nanoclusters • Cd(stearate)2 + (octyl)3PO + high temperature solvent octadecylamine • Reaction temperature 310-330°C • Se + (octyl)3P • Mixing temperature 270-300°C • Provides TOPO capped core nanocluster precursor (CdSe)n(TOPO)m

  15. SYNTHESIS OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS • Add ZnEt2 + (octyl)3P in controlled stoichiometry increments • Mixing temperature 290-320°C • Add Se + (octyl)3P • Mixing temperature 270-300°C • Monitor photoluminescence until constant wavelength emission • Desired TOPO capped core-corona nanocluster product (ZnxCd1-xSe)n(TOPO)m

  16. TEM OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS SHOWS MONOTONIC INCREASE IN DIAMETER OF NANOCRYSTALS WITH ADDITION OF ZnSe CORONA TO CdSe CORE SPATIALLY RESOLVED EDX SHOWS NANOCRYSTAL COMPOSITIONAL HOMOGENIETY

  17. ABSORPTION-EMISSION SPECTRA OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALSEXPECTED BLUE SHIFT OF ABSORPTION AND EMISSION WITH INCREASING AMOUNTS OF WIDE BAND GAP ZnSe COMPONENT IN NARROW BAND GAP CdSe NANOCRYSTALS

  18. PXRD PATTERNS OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALSEXPECTED LINEAR VEGARD LAWDECREASE IN UNIT CELL DIMENSIONS (nl = 2dsin) WITH INCREASING AMOUNTS OF SMALLER UNIT CELL ZnSe COMPONENT IN LARGER UNIT CELL CdSe NANOCRYSTALS

  19. MODE OF FORMATION OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS Effect of Different Reaction Temperatures – first Ostwald ripening larger ones grow at expense of smaller nanocrystals - driven by smaller surface free energy – second diffusive mixing alloying across interface - third reaction to form solid solution

  20. SYNTHESIS OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS • High structural and optical quality ZnxCd1-xSesemiconductoralloy nanocrystals prepared using core-corona precursor made by growing stoichiometric amounts of Zn and Se on surface of pre-prepared CdSe nanocrystal seeds and thermally inducing alloy nanocluster formation by interdiffusion of element components within nanocluster - diffusion length control of reaction between two solid reagents • With increasing Zn content, a composition-tunable photoemission across most of the visible spectrum has been demonstrated by a systematic blue-shift in emission wavelength (QSE) demonstrating alloy nanocluster formation and not phase separation • A rapid alloying process is observed at the “alloying point” as the core and corona components mix to provide a homogeneous linear Vegard law type distribution of elements in the nanoclusters

  21. Functional device, LED, laser, sensor, biolabel Ligand capping arrested growth of nanocluster core Growth and ligand capping of nanocluster core High T solvent, ligand, protection, amphiphilic amines, carboxylic acids, phosphines, phosphine oxides, phosphonic acids Inorganic precursor, oxides, sulphides, metals, nucleation of nanocluster seed

  22. ARRESTED GROWTH OF MONODISPERSED NANOCLUSTERSCRYSTALS, FILMS AND LITHOGRAPHIC PATTERNS nMe2Cd + nnOct3PSe + mnOct3PO  (nOct3PO)m(CdSe)n + n/2C2H6

  23. Addition of reagent BASICS OF RAPID MIXING OF PRECURSORS, NANOCLUSTER NUCLEATION SEED FORMATION, NANOCRYSTAL GROWTH, CRYSTALLIZATION AND CAPPING STABILIZATION Gb > Gs supersaturation nucleation aggregation capping and stabilization

  24. Absorption Spectra

  25. Phospholuminescence Spectra

  26. EgC = EgB + (2h2/8R2)(1/me* + 1/mh*) - 1.8e2/R Quantum localization term Coulomb interaction between e-h CAPPED MONODISPERSED SEMICONDUCTOR NANOCLUSTERS TUNING CHEMICAL AND PHYSICAL PROPERTIES OF MATERIALS WITH SIZE AS WELL AS COMPOSITION AND STRUCTURE nMe2Cd + nnOct3PSe + mnOct3PO  (nOct3PO)m(CdSe)n + n/2C2H6

  27. THINK SMALL DO BIG THINGS!!! EgC = EgB + (2h2/8R2)(1/me* + 1/mh*) - 1.8e2/R tuning chemical and physical properties of materials with size as well as composition and structure

  28. 2 MoCl5 + 5 Na2S  2 MoS2 + 10 NaCl + S Richard Kaner Rapid Solid State Synthesis of Materials

  29. RAPID SOLID STATE PRECURSOR SYNTHESIS OF MATERIALSLixQy + MClx MQy + xLiClMETATHESIS METAL EXCHANGE REACTIONQ = N, P, As (PNICTIDES)S, Se, Te (CHALCOGENIDES)C, Si (CARBIDES, SILICIDES)

  30. RAPID SS PRECURSOR SYNTHESIS OF MATERIALS LixQy + MClx MQy + xLiCl METATHESIS METAL EXCHANGE REACTIONQ = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES) • Many useful materials, such as ceramics, are most often produced from high temperature reactions (500-3000°C) between solid reagents which often take many days due to the slow nature of solid-solid diffusion. • Rapid SS new method enables high quality refractory materials to be synthesized in seconds from appropriate solid state precursors. • Basic idea is to react stable high oxidation state metal halides with alkali or alkaline earth compounds in a metathesis metal exchange reaction to produce the desired product plus an alkali(ne) halide salt which can simply be washed away. • Since alkali(ne) salt formation is very favorable many of these reactions are thermodynamically downhill by 100-200 kcal/mol or more.

  31. RAPID SS PRECURSOR SYNTHESIS OF MATERIALS LixQy + MClx MQy + xLiClMETATHESIS METAL EXCHANGE REACTIONQ = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES) • MoS2, a layered material with VDW interlayer forces used as a lubricant in low T,P aerospace applications, as a cathode for rechargeable LSSB and as a hydrodesulfurization catalyst for removing S from organosulfur compounds, is normally prepared by heating the elements Mo/S to 1000°C for several days • New SSS gives pure crystalline MoS2 from a self-initiated reaction between the solids MoCl5 and Na2S in seconds!!! • 2 MoCl5 + 5 Na2S  2 MoS2 + 10 NaCl + S • NaCl byproduct is simply washed away. • Other layered transition MS2 can be produced in analogous rapid solid-solid reactions: M = W, Nb, Ta, Rh • Na2Se used for MSe2 syntheses

  32. PARTICLE SIZE CONTROL USE AN INERT DILUENT LIKE NaCl TO AMELIORATE THE HEAT OF REACTION, CONTROL NUCLEATION AND LIMIT THE GROWTH OF PARTICLES • MoCl5/NaCl MoS2 Particle Size nm • 1:045 • 1:4 18 • 1:168 • NaCl washed away after reaction • Leaves behind insoluble product nano MoS2

  33. RAPID SS PRECURSOR SYNTHESIS OF MATERIALS LixQy + MClx MQy + xLiClMETATHESIS METAL EXCHANGE REACTIONQ = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES) • High quality anion solid solutions such as MoS1-xSex can be made using the precursor Na2S1-xSex formed by co-precipitation of Na2S/Na2Semixtures from liquid ammonia • High quality cation solid solutions such as Mo1-xWxS2 can be made by melting together the metal halides MoCl5 and WCl6, followed by reaction with Na2S • The solid-solution products can be analyzed by studying the MoW alloys formed after reduction in hydrogen - ASSUMING NO SEGREGATION!!!

  34. SOLID SOLUTION PRECURSORS • REACTANT A REACTANT B • Na2(S,Se) GaCl3 • Na3(P,As) MoCl5 • WCl6 • PRODUCT • Ga(P,As) • Mo(S,Se)2 • W(S,Se)2 • (Mo,W)S2

  35. RAPID SS PRECURSOR SYNTHESIS OF MATERIALS: LixQy + MClx MQy + xLiClMETATHESIS METAL EXCHANGE REACTIONQ = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES) • These SS metathesis reactions are becoming a general process for synthesizing important materials. • For example, refractory ceramics such as ZrN (m.p. ~ 3000°C) can be produced in seconds from ZrCl4 and Li3N • ZrCl4 + 4/3Li3N  ZrN + 4LiCl + 1/6N2 • NOTE CHANGE IN OXIDATION STATE Zr(IV) REDUCED TO Zr(III) WITH OXIDATION OF N(-III) TO N(0) • MoSi2, a material used in high temperature furnace elements, can be made from MoCl5 and Mg2Si

  36. RAPID SS PRECURSOR SYNTHESIS OF MATERIALS: LixQy + MClx MQy + xLiClMETATHESIS METAL EXCHANGE REACTIONQ = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES) • The III-V SCs GaP and GaAs can be made in seconds from the solid precursors GaCl3 and Na3P or Na3As • GaCl3 + Na3As  GaAs + 3NaCl • Recently, high pressure methods have been employed to allow the use of metathesis to synthesize gallium nitride (GaN) using Li3N and GaCl3 • Very important blue laser diode material, a synthesis which was not possible using the methods for GaP or GaAs

  37. SUMMARIZING KEY FEATURES OF RAPID SOLID STATE SYNTHESIS OF MATERIALS • Metathesis – metal exchange pathway • Access to large number of materials • Extremely rapid about 1 second!!! • Initiated at or near RT – rapid rise in reaction temperature • Self-initiated self-propagating • Thermodynamic driving force of DGo alkali(ne) halides • Control of particle size with inert alkali(ne) halide matrix • Solid solution materials synthesis feasible • Most recent addition to metathesis zoo are carbides

  38. METAL CARBIDES - TRY TO BALANCE THESE EQUATIONS - OXIDATION STATE CHALLENGE • 3ZrCl4 + Al4C3  3ZrC + 4AlCl3 • 2WCl4 + 4CaC2  2WC + 4CaCl2 + 6C • 2TiCl3 + 3CaC2 2TiC + 3CaCl2 + 4C • DO NOT CONFUSE CARBIDE C4- IN Al4C3 FROM ACETYLIDE (C22-) IN CaC2!!! • Inert, hard, refractory, electrically conducting ceramics • Cutting tools, crucibles, catalysts, hard steel manufacture

  39. Search for Superhard Materials • Search for new ultra-incompressible superhard materials with mechanical properties that rival those of diamond is an exciting and active area of research. • Such new materials are extremely useful as abrasives, cutting tools and coatings because of (i) the inability of diamond to effectively cut Fe, Co, Ni (soluble in and forms carbides at high temperature) and (ii) the high cost of synthesizing diamond or diamond substitutes, such as cubic boron nitride (c-BN). • Both Diamond and c-BN must be synthesized under high pressure and high temperature (HPHT) conditions. Advanced Functional Materials Oct 2009 asap web

  40. Superhard Cubic BN Hexagonal BN Synthesis Direct Reaction 900C B2O3 + 2NH3 → 2BN + 3H2O B(OH)3 + 3NH3 → BN + 2NH3 + 3H2O Cubic BN obtained from hexagonal BN by crystallization at 5-18 GPa and 1730-3230C

  41. Mechanical Properties Basics • Elastic stiffness or compressibility of a material is dependent on elastic coefficients quantified by the bulk modulus B - resistance of a solid to volume compression under hydrostatic stress (isotropic pressure) • B = V(dp/dv) • p is the pressure, v is the volume so bulk modulus is thus simply the inverse of the fractional volume change with pressure.

  42. Mechanical Properties Basics • Bulk modulus of a material related to molar volume (Vm) and cohesive energy (Ec) : • B = Ec/Vm • Search for superhard ultra-incompressible materials with small molar volumes and strong interatomic forces resulting from high cohesive energies tend to have high bulk moduli

  43. Similar Trend of Cohesive Energies of the Elements and their Bulk Moduli

  44. Metathesis Metal Exchange Synthesis of Metal Diborides • Design principle for discovering superhard ultra-incompressible materials – combine high bulk modulus metals like Os, Re, Ru with small strongly covalently bonded elements like B • OsCl3 and ReCl3 halide source materials with MgB2 – highly exothermic reaction works under atmospheric pressure in seconds – wash away magnesium dichoride and chlorine gas evolved • 2MCl3 + 2MgB2 2MB2 + 2MgCl2 + Cl2

  45. Precursor MgB2 Mg B Mg Note basic repeat unit is 1Mg + 6/3B = MgB2

  46. Superhard OsB2 • Puckered B22- six ring sheets with strong directional B-B bonding • Integrated with double layers of Os(II) with strong Os-B directional bonds • Anisotropic structure induces anisotropic mechanical properties • Stronger along c axis compared to ab plane where Os double layers can slide wrt one another

  47. Superhard ReB2 • Puckered B22- six ring sheets with strong directional B-B bonding • Integrated with single layers of Re(II) with strong Re-B directional bonds • Anisotropic structure induces anisotropic mechanical properties

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