magnetic garnets, y x gd 3-x fe 5 o 12 tunable magnetic perovskites y(no 3 ) 3 + gd(no 3 ) 3 + fecl...
TRANSCRIPT
![Page 1: MAGNETIC GARNETS, Y x Gd 3-x Fe 5 O 12 TUNABLE MAGNETIC PEROVSKITES Y(NO 3 ) 3 + Gd(NO 3 ) 3 + FeCl 3 + NaOH Y x Gd 3-x Fe 5 O 12 Mixed metal hydroxide](https://reader035.vdocuments.mx/reader035/viewer/2022081515/56649ee55503460f94bf52c1/html5/thumbnails/1.jpg)
MAGNETIC GARNETS, YxGd3-xFe5O12
TUNABLE MAGNETIC PEROVSKITES
• 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, enables UC dimensions to be determined as a function of Y: Ga ratio over range 0 < x < 3
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PXRD OF SOLID PRODUCTS OF Y(NO3)3 + Gd(NO3)3 + FeCl3 + NaOH REACTION
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HYDROTHERMAL SYNTHESIS AND CRYSTAL GROWTH OF YTTRIUM GADOLINIUM IRON GARNET
Fe2O3
Seed crystal to grow YxGd3-xFe5O12 crystal
Gd2O3 /Y2O3
baffles
aqueous basic medium, mineralizes, temperature gradient transports, deposits reactants on seed crystal to grow product yttrium gadolinium iron oxide crystal
T2 T1 T2
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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)
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ONE OCTANT OF CUBIC UNIT CELL OF Y3Al5O12 (YAG)
One octant of cubic unit cell of garnet
Faces 3 dodecahedral Y(3+) sites
Corners and center 2Oh AlO6 sites
Faces 3Td AlO4 sites
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GARNETS DISPLAY INTERESTING COOPERATIVE MAGNETIC BEHAVIOR
• C3A2D3O12 isomorphous 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
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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
6. Ordered superlattice of two components - ED
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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 average P of the end-member materials
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MAGNETIC GARNETS, YxGd3-xFe5O12
TUNABLE MAGNETIC MATERIALS
• Cubic unit cell parameter a versus x for YxGd3-xFe5O12
• Composition Lattice 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 1.2468R(Gd(3+)) = 0.938Å > R(Y(3+)) = 0.900Å
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MAGNETIC GARNETS, YxGd3-xFe5O12
TUNABLE 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
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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
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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
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VEGARD LAW AT THE NANOSCALE
SYNTHESIS OF COMPOSITION TUNABLE MONODISPERSE CAPPED ZnxCd1-xSe ALLOY NANOCRYSTALS
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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 core nanocluster precursor (CdSe)n(TOPO)m
• Add ZnEt2 + (octyl)3P in controlled stoichiometry increments • Mixing temperature 290-320°C
• Monitor photoluminescence until constant wavelength emission
• Desired core-corona nanocluster product (ZnxCd1-xSe)n(TOPO)m
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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
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ABSORPTION-EMISSION SPECTRA OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS
EXPECTED BLUE SHIFT OF ABSORPTION AND EMISSION WITH INCREASING AMOUNTS OF WIDE BAND GAP ZnSe COMPONENT IN
NARROW BAND GAP CdSe NANOCRYSTALS
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PXRD PATTERNS OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS
EXPECTED LINEAR VEGARD LAW DECREASE IN UNIT CELL DIMENSIONS WITH INCREASING AMOUNTS OF SMALLER UNIT CELL
ZnSe COMPONENT IN LARGER UNIT CELL CdSe NANOCRYSTALS
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MODE OF FORMATION OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS
Effect of Different Reaction Temperatures
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SYNTHESIS OF COMPOSITION TUNABLE ZnxCd1-xSe ALLOY NANOCRYSTALS
• High structural and optical quality ZnxCd1-xSe semiconductor alloy nanocrystals successfully 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
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ARRESTED GROWTH OF MONODISPERSED
NANOCLUSTERS
CRYSTALS, FILMS AND LITHOGRAPHIC
PATTERNS
nMe2Cd + nnOct3PSe + mnOct3PO (nOct3PO)m(CdSe)n + n/2C2H6
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Additionof reagent
nucleation
aggregation
BASICS OF NANOCLUSTER NUCLEATION, GROWTH, CRYSTALLIZATION AND CAPPING STABILIZATION
capping and stabilization
nMe2Cd + nnOct3PSe + mnOct3PO (nOct3PO)m(CdSe)n + n/2C2H6
Gb > Gs
supersaturation
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Spatial and quantum confinement and dimensionality
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CAPPED MONODISPERSED SEMICONDUCTOR NANOCLUSTERS
nMe2Cd + nnOct3PSe + mnOct3PO (nOct3PO)m(CdSe)n + n/2C2H6
EgC = Eg
B + (h2/8R2)(1/me* + 1/mh*) - 1.8e2/R
Coulomb interaction between e-h
Quantum localization term
TUNING CHEMICAL AND PHYSICAL PROPERTIES OF MATERIALS WITH SIZE AS WELL AS COMPOSITION AND STRUCTURE
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THINK SMALL DO BIG THINGS!!!
EgC = Eg
B + (h2/8R2)(1/me* + 1/mh*) - 1.8e2/R
tuning chemical and physical properties of materials with size as well as composition and structure
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2 MoCl5 + 5 Na2S 2 MoS2 + 10 NaCl + S
Richard Kaner: Rapid Solid State Synthesis of Materials
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RAPID SS PRECURSOR SYNTHESIS OF MATERIALS LixQy + MClx MQy + xLiCl METATHESIS METAL EXCHANGE REACTION
Q = 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) 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.
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• 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
RAPID SS PRECURSOR SYNTHESIS OF MATERIALS LixQy + MClx MQy + xLiCl METATHESIS METAL EXCHANGE REACTION
Q = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES)
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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
• 1:0 45
• 1:4 18
• 1:16 8
• NaCl washed away after reaction
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• High quality anion solid solutions such as MoS1-xSex can be made using the precursor Na2S1-xSex formed by co-precipitation of Na2S/Na2Se mixtures 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!!!
RAPID SS PRECURSOR SYNTHESIS OF MATERIALS LixQy + MClx MQy + xLiCl METATHESIS METAL EXCHANGE REACTION
Q = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES)
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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
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• 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
RAPID SS PRECURSOR SYNTHESIS OF MATERIALS: LixQy + MClx MQy + xLiCl METATHESIS METAL EXCHANGE REACTION
Q = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES)
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• The III-V SCs GaP and GaAs can be made in seconds from the solid precursors GaCl3 and Na3P or Na3As
• 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
RAPID SS PRECURSOR SYNTHESIS OF MATERIALS: LixQy + MClx MQy + xLiCl METATHESIS METAL EXCHANGE REACTION
Q = N, P, As (PNICTIDES), S, Se, Te (CHALCOGENIDES), C, Si (CARBIDES, SILICIDES)
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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 Go 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
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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 (C2
2-) IN CaC2!!!
• Inert, hard, refractory, electrically conducting ceramics
• Cutting tools, crucibles, catalysts, hard steel manufacture