[PPT] - Thermoelectric features and magnetic properties of Pr { Fe , Co , Ni PowerPoint Presentation

SLIDE 1

Hvar Workshop on Correlated Thermoelectrica, September 2005

Thermoelectric features and magnetic properties of Pr{Fe, Co, Ni}4Sb12

E. Bauer

Institute of Solid State Physics A - 1040 Wien, Austria

26. September 2005

in cooperation with:

St. Berger, G.Hilscher, R. Lackner, H. Michor, Ch. Paul,
M. Reissner, W. Steiner A. Grytsiv and P. Rogl, Vienna, Austria
E. Scheidt, Augsburg, Germany

A.D. Hillier, D.T. Adroja, ISIS, UK

SLIDE 2

Hvar Workshop on Correlated Thermoelectrica, September 2005

Thermoelectric features and magnetic properties of Pr{Fe, Co, Ni}4Sb12

E. Bauer

Institute of Solid State Physics A - 1040 Wien, Austria

26. September 2005

in cooperation with:

St. Berger, G.Hilscher, R. Lackner, H. Michor, Ch. Paul,
M. Reissner, W. Steiner A. Grytsiv and P. Rogl, Vienna, Austria
E. Scheidt, Augsburg, Germany

A.D. Hillier, D.T. Adroja, ISIS, UK

SLIDE 3

Motivation and Overview

Thermoelectric conversion: complex multinary compounds for

– large values of the Seebeck coefficient S – high Peltier coefficients ΠI = STI

Knowledge of principal interaction mechanisms
Requirements for thermoelectricas and scenarios for possible

improvements

Dominating role of rare earth ions for ground state properties

– Superconductivity – Heavy Fermion behaviour – Metal to insulator transitions – Mixed and intermediate valence

SLIDE 4

Formation of skutterudites

SLIDE 5

Formation of skutterudites

Formation of Skutterudites EpT4X12

H X' X X" He Li Be B C N O F Ne Na Mg T' T T" Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Ku Ns La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

7 subgroups
stable

binaries with Co, Rh, Ir and P, As, Sb

72 compensated

electrons ⇒ dia- magnetic semi- conductors

ternaries

are electronically stabilised.

SLIDE 6

Formation of skutterudites

SLIDE 7

Formation of skutterudites

unfilled skutterudites

binary ternary T4X12 T'4X12 T"4X12 T2X'6X"6 T'2T"2X12 T'4X8X"4 T"4X8X'4 Co4P12 Co4As12 Co4Sb12 Rh4P12 Rh4As12 Rh4Sb12 Ir4P12 Ir4As12 Ir4Sb12 “Fe4Sb12” Ni4P12 Pd4P12 Co4Ge6Te6 Co4Sn6Se6 Co4Sn6Te6 Co4Ge6S6 Co4Ge6Se6 Rh4Ge6S6 Ir4Ge6S6 Ir4Ge6Se6 Ir4Sn6S6 Ir4Sn6Se6 Ir4Sn6Te6 Fe2Ni2Sb12 Fe2Ni2As12 Fe2Pd2Sb12 Fe2Pt2Sb12 Ru2Ni2Sb12 Ru2Pd2Sb12 Ru2Pt2Sb12 Fe4Sb8Se4 Fe4Sb8Te4 Ru4Sb8Se4 Ru4Sb8Te4 Os4Sb8Te4 Ni4P8Ge4 Ni4Bi8Ge4 Pt4Sb7.2Sn4.8 Ni4Sb8Sn4 Ni4As8Ge4

filled skutterudites

ternary Quaternary EpT4X12 EpT'4(X1-xX'x)12 Ep(T1-xT'x)4X12 T = Fe, Ru, Os T' = Co, Ir T = Fe; T' = Co X = P, As, Sb X = Sb; X' =Ge, Sn X = Sb Ep=Ca, Sr, Ba, La, Ce, Pr, Nd Ep = La, Nd, Sm, Tl Ep = Tl Sm, Eu, Gd, Tb, Yb, Th, U LaIr4Sb9Ge3,NdIr4Sb9Ge3, TlFeCo3Sb12 LaFe4P12, UFe4P12, ThOs4As12, YbFe4Sb12, ... SmIr4Sb9Ge3,TlCo4Sb11Sn, La0.9Co4Sb10.3Sn2.44, ….

metastable partially filled skutterudites:

Ep1-yFe4Sb12; Ep = Na,Y, Hf, Sn, Lu Ep1-yCo4Sb12; Ep = Sn, Pb

7 subgroups
stable

binaries with Co, Rh, Ir and P, As, Sb

72 compensated

electrons ⇒ dia- magnetic semi- conductors

ternaries

are electronically stabilised.

SLIDE 8

Filled skutterudites

SLIDE 9

Filled skutterudites

a b c x y z

el.positive element (e.g. Pr, Nd ) Sb, (P,As) d-element (Fe, Co, Rh ...)

structure type: LaFe4P12

(CoAs3-structure).

lattice parameter:

a = 9.127 ˚ A (PrFe4Sb12)

a strongly dependent on

pnictogen atom (change as large as 15 % )

RE ion sixfold co-ordinated

by X.

extremely large atomic dis-

placement parameter of fil- ler elements; increases with increasing cage volume; in- creases with decreasing io- nic size.

SLIDE 10

Pr-based skutterudites

SLIDE 11

Pr-based skutterudites

superconductivity in PrRu4As12 (Shirotani et al., 1997) and

PrRu4Sb12 below 2.4 and 1 K (Takeda et al., 2000);

a metal to insulator - and structural phase transition in

PrRu4P12 at TMI = 60 K Sekine et al., 1997, Lee et al., 2001,

Magnetic ordering at TN = 6.2 K in PrFe4P12 (Torikachvili et

al., 1987) . But: antiquadrupolar order parameter? (Hao et al., 2002) – Kondo-like anomalies; Cp/T for T → 0 shows a huge value

f about 1.4 J/molK2 (Sato et al., Matsuda et al., 2000).

– de Haas van Alphen measurements evidenced extraordinary heavy electrons m ≈ 70m0 (Sugawara et al., 2001), suggesting strongly correlated electrons.

Superconductivity and heavy fermion behaviour in PrOs4Sb12

(E.D. Bauer et al., 2001). Tc = 1.8 K; Γ3 non-magnetic ground state.

SLIDE 12

Electronic features and interactions of filled skutterudites

SLIDE 13

Electronic features and interactions of filled skutterudites

Hybridisation and band positions in skutterudites (Harima 2001)

Kondo effect (Ce, Yb, Pr!);
RKKY interaction;
crystal field splitting;

– non-magnetic CEF ground state possible for non-Kramers ions, e.g. Pr; – quadrupolar moment 3J2

z − J(J + 1) possible;

p − f mixing plays a crucial

role

large coordination number in

skutterudites

SLIDE 14

Magnetic order in Pr0.73Fe4Sb12

5 10 15 20 25 30 0.0 2.0e-5 4.0e-5 6.0e-5 8.0e-5 1.0e-4 1.2e-4

χa.c. [m3/kg] T [K]

Pr0.73Fe4Sb12

T [K]

5 10 15 20 25 30

1/χ [mole/emu]

2 4 6 8 10 12 14

Magnetic pha-

se transition at Tmag = 4.5 K;

Order

associa- ted with locali- zed Pr-4f elec- trons;

SLIDE 15

Magnetic order in Pr0.73Fe4Sb12

SLIDE 16

Magnetic order in Pr0.73Fe4Sb12

µ0H [T]

1 2 3 4 5 6

M [µB/f.u.]

0.0 0.5 1.0 1.5 2.0

T = 2 K

5 10 15 20 25 30 0.0 2.0e-5 4.0e-5 6.0e-5 8.0e-5 1.0e-4 1.2e-4

χa.c. [m3/kg] T [K]

Pr0.73Fe4Sb12

T [K]

5 10 15 20 25 30

1/χ [mole/emu]

2 4 6 8 10 12 14

Pr0.73Fe4Sb12

no spontaneous

magnetisation → AFM?!

Absence
f

saturation in M(H) at 6 T

Reduced

value

f 2.6 µB at 6

T compared to free Pr3+ with gµBJ = 3.2 µB

SLIDE 17

Magnetic order in Pr0.73Fe4Sb12: elastic neutron scattering (ROTAX at ISIS)

SLIDE 18

Magnetic order in Pr0.73Fe4Sb12: elastic neutron scattering (ROTAX at ISIS)

no

resolveable in- tensity between low and high tempera- tures - neither at nuclear Bragg peaks (FM state) nor at additional (hkl) va- lues (AFM).

FM more likely
some

corroboration by B. Maples group.

SLIDE 19

Magnetic order in Pr0.73Fe4Sb12: µSR spectroscopy at ISIS

Tim e (µs) 1 2 3 4

Asymmetry

0.05 0.10 0.15 0.20 0.25 0.30

ZF 0.03K 15K 15K 6K 5K 4.6K 3.6K 2K 0.03K

zero field µSR spectra at various temperatures

damping at high tem-

peratures dominated by static nuclear mo- ments;

decay

functi-

n:

G(t) = a exp(−λt)KT(−σKTt) T = 15 K: λ = 0.045 µs−1, σKT = 0.14 µs−1

damping rate σ increa-

ses with decreasing T.

NO sign of frequency

fluctuations due to Pr

rdering!

SLIDE 20

Magnetic order in Pr0.73Fe4Sb12: µSR spectroscopy at ISIS

Time (µs) 1 2 3 4

Asymmetry

0.05 0.10 0.15 0.20 0.25 0.30

0G 50G 100G 300G 700G 2500G T=0.03K

µSR spectra at various external fields at 0.03 K.

a minimum and a ma-

ximum evolves bet- ween 50 and 700 G Conclusions: complex ma- gnetic structure with re- duced moments; or qua- drupolar degrees of free- dom?!

SLIDE 21

Paramagnetic properties of Pr0.73Fe4Sb12

T [K]

50 100 150 200 250

1/χ [mol/emu]

20 40 60 80 100 120 140 160

Pr0.73Fe4Sb12, raw data Pr0.73Fe4Sb12, corected for Fe

Curie-Weiss behavior of

1/χ(T) with µeff=4.15 µB; µeff(Pr3+) = 3.58 µB

small positive paramagne-

tic Curie temperature → FM?

Deviation

from Curie- Weiss at lower tempera- tures ⇒ CEF effects

Correction of data accor-

ding to χ = χPr + χ[Fe4Sb12] ⇒ isolation of χPr

Extrapolation to 100% Pr

SLIDE 22

Crystal electric field effects: basics

x-axis y-axis Rare earth RE3+ ri Rj R (4f)N = (nl)N Qj Charge distribution ρ(R)

ground state multiplet j = 5/2 (e.g., Ce, Sm) N = 2j+1 = 6 energy e.g., hexagonal symmetry cubic symmetry e.g., |1/2 > e.g., |3/2 > e.g., |5/2 > Γ7 Γ8

HCF|Ψ = E|Ψ with HCF =

l,m

Bm

l Om l

Bm

l

. . . crystal field parameters (to be determined by experiment or theory); Om

l

. . . Stevens Operators Hhexa

CF

= B0

2O0 2 + B0 400 4 + B0 6O0 6

SLIDE 23

Crystal electric field effects: basics

SLIDE 24

Crystal electric field effects: basics

x-axis y-axis Rare earth RE3+ ri Rj R (4f)N = (nl)N Qj Charge distribution ρ(R)

ground state multiplet j = 4 (e.g., Pr) N = 2j+1 = 9 energy e.g., cubic symmetry Γ3 Γ4 Γ1 Γ5

HCF|Ψ = E|Ψ with HCF =

l,m

Bm

l Om l

Bm

l

. . . crystal field parameters (to be determined by experiment or theory); Om

l

. . . Stevens Operators Hcub.

CF = B0 4

O0

4 + 5O4 4

+ B0

6

O0

6 − 21O6 6

SLIDE 25

CEF derived susceptibility Pr0.73Fe4Sb12

Susceptibility related to Pr: 1/χ = 1/χCF − λ; χCF crystal field susceptibility, λ molecular field parameter. Hamiltonian for cubic systems: Hcub = B0

4(O0 4+O4 4)+B0 6(O0 6−21O4 6)

Fit:B0

4 = 0.04K; B0 6 = 0.0013K.

Γ5 (triplet) = 0 K ⇒ Γ1 (singlet) = 28 K ⇒ Γ4 (triplet) = 136 K ⇒ Γ3 (doublet) = 215 K. Van Vleck formula: χCF

α

= NA(gjµB)2

n exp(−En/kBT)
r,s

|r|Jα|s|2 exp −Er kBT exp((Er − Es)/kBT) − 1 Er − Es

SLIDE 26

CEF derived susceptibility Pr0.73Fe4Sb12

T [K]

50 100 150 200 250

1/χ [mol/emu]

20 40 60 80 100 120 140 160 180 200

CEF calc.:

T,Th

CEF calc.:

cub

Pr0.73Fe4Sb12

T [K]

25 50 75 100 125

1/χ [mol/emu]

20 40 60 80

Pr0.73Fe4Sb12 Pr0.73Fe4Sb12 corr., see text Γ4

2

Γ4

1

Γ3 Γ1 Γ3 Γ1 Γ4 Γ5

194 K 123.5 K 24.5 K 0 K 215 K 136 K 28 K 0 K

cub T,Th

|<Γ5|Jz|Γ1>|2 = 0 |<Γ4

2|Jz|Γ1>|2 = 0

distinct features of

skutterudite struc- ture causes modi- fication of simple cubic CEF Hamil- tonian; → mixing

f states Γ4 and Γ5
slight

changes in energy

|Γ2

4|Jz|Γ1|2 = 0

Hcub recalc. for cub. point groups T and Th (Takegahara, 2001): HT,Th = B0

4(O0 4 + 5O4 4) + B0 6(O0 6 − 21O4 6) + B2 6(O2 6 − O6 6)

SLIDE 27

Inelastic neutron scattering in Pr0.73Fe4Sb12

SLIDE 28

Inelastic neutron scattering in Pr0.73Fe4Sb12

Energy transfer [meV]

10
5

5 10 15 20

Scattering function (Q,ω) [a.u.]

2 4 6 8

exp. data points

sum elastic peak peak at 10.7 meV peak at 16.8 meV

Pr0.73Fe4Sb12

T = 10 K 40 meV incident beam x 80

Inelastic peaks at:

10.7 meV ←

→ 124 K

16.8 meV ←

→ 195 K

Energy transfer [meV]

2
1

1 2 3 4 5 6 7

Scattering function (Q,ω) [a.u.]

1 2

exp. data points

sum elastic peak quasielastic peak peak at 2.1 meV

Pr0.73Fe4Sb12

T = 10 K 11 meV incident beam

Inelastic peaks at:

2.1 meV ←

→ 24 K Verification: comparison of inten- sity and transition probability Excitation at ≈ 2.1 meV requires description using modified CEF Hamiltonian: |Γ2

4|Jz|Γ1|2 = 0

SLIDE 29

Electrical resistivity of REyFe4Sb12, RE = Pr, Nd

SLIDE 30

Electrical resistivity of REyFe4Sb12, RE = Pr, Nd

ρspd = const · m∗J2(gj − 1)2

ms,m′

s,i,i′

m′

si′|

s j|msi2pifii

with pi = exp[−Ei/kBT]/

j exp[−Ej/kBT] and

fii = 2/[1 + exp[−((Ei − E′

i)/kBT)]]

T [K]

50 100 150 200 250

ρ [µΩcm]

100 200 300 400 500 600 700 800

Nd0.72Fe4Sb12 Pr0.73Fe4Sb12 La0.83Fe4Sb12

20 40 60 80 100

ρ/ρ100 K

0.2 0.4 0.6 0.8 1.0 1.2

T [K]

Pr0.73Fe4Sb12, exp. data ρCF B4

0 = 0.04 K,

B6

0 = 0.0012 K

(a) (b)

ρ(T)

exhibits signature

f

magnetic phase transition and strong crystal field in- fluence in the paramagnetic temperature range.

Problem: definition of an ap-

propriate phonon contributi-

n ρph to derive ρspd.

SLIDE 31

SLIDE 32

Heavy quasi-particles: Specific heat of Pr0.73Fe4Sb12

Tmag = 5.5 K;
magnetic order suppressed by

magnetic fields (µ0H ≥ 3 T);

signs for a field-induced NFL

behaviour?

SLIDE 33

Heavy quasi-particles: Specific heat of Pr0.73Fe4Sb12

Tmag = 5.5 K;
magnetic order suppressed by

magnetic fields (µ0H ≥ 3 T);

signs for a field-induced NFL

behaviour?

huge

nuclear contribution (primarily Pr, I = 5/2);

T ≈ 1 K: Cp/T

increases with increasing field;

mechanism:

fluctuations

f

the order parameter prior to a phase transition or suppres- sion of magnetic order.

SLIDE 34

Characteristic temperature and entropy of Pr0.73Fe4Sb12

SLIDE 35

Characteristic temperature and entropy of Pr0.73Fe4Sb12

Tchar ≈ 25 K
reduced jump of Cp at T =

Tmag - well known feature

f Kondo systems (δCp[T =

Tord] decreases with increa- sing field and vanishes beyond a critical value).

Entropy at 15 K in perfect

agreement with CEF sche- me Stheor

mag (T

= 15 K) = 10 J/molK!

magnetic Γ5 ground state

SLIDE 36

Crystallography of Pr(Fe, Co, Ni)4Sb12

SLIDE 37

Crystallography of Pr(Fe, Co, Ni)4Sb12

linear decrease
f lattice para-

meter with in- creasing Co, Ni content

content of co,

Ni related to Pr filling

linear

decrea- se

f

lattice constant with decreasing Pr content

SLIDE 38

Magnetic properties of Pr(Fe, Co, Ni)4Sb12

positive slope in

1/χ → sub- stantial diama- gnetic contri- bution

charge

com- pensation approached χmeas = χpara + χdia. and µmeas

eff =

y(µPr3+

eff )2 + (µ[Fe4−xTxSb12] eff

)2

SLIDE 39

Magnetic properties of Pr(Fe, Co, Ni)4Sb12

µmeas

eff

θp µPr3+

eff

µsub

eff

χ0 χmeas

300K

χtheor

dia

[µB] [K] [µB] [10−3 emu/mol)] Pr0.73Fe4Sb12 4.15 5.45 3.06 2.81

Pr0.57Fe3.5Ni0.5Sb12

3.26

8.13

2.70 1.82 0.273

Pr0.42Fe3NiSb12

2.35

10.40

2.32 0 (0.37)

Pr0.21Fe2.5Ni1.5Sb12

1.98

22.77

1.64 1.11

0.492

0.9458 ∼ -0.230 Pr0.62Fe3CoSb12 3.52

17.6

2.82 2.11 0.0008

Pr0.25FeCo3Sb12

2.16

15.84

1.79 1.21

0.537

1.2663 ∼ -0.230 Pr0.5Co4Sb10Sn2 2.63

12.46

2.53 0 (0.71)

χmeas = χpara + χdia.

and µmeas

eff =

y(µPr3+

eff )2 + (µ[Fe4−xTxSb12] eff

)2

SLIDE 40

Specific heat of Pr(Fe, Co, Ni)4Sb12

SLIDE 41

Specific heat of Pr(Fe, Co, Ni)4Sb12

order

evi- dent for Pr0.73Fe4Sb12

order and large

Sommerfeld values sup- pressed upon Fe/(Fe,Co) substitution

unexpected

anomaly for Pr0.25FeCo3Sb12

SLIDE 42

Specific heat of Pr(Fe, Co, Ni)4Sb12

SLIDE 43

Specific heat of Pr(Fe, Co, Ni)4Sb12

field

response different for Pr0.73Fe4Sb12 and Pr0.25FeCo3Sb12; different kind

f

phase transition.

SLIDE 44

Temperature dependent resistivity of Pr(Fe, Co, Ni)4Sb12

SLIDE 45

Temperature dependent resistivity of Pr(Fe, Co, Ni)4Sb12

increasing
verall

resis- tivity upon Fe/(Co,Ni) substitution

hole

driven transport in Pr0.73Fe4Sb12 becomes com- pensated → semiconducting like behaviour

SLIDE 46

Temperature dependent resistivity of Pr(Fe, Co, Ni)4Sb12

SLIDE 47

Temperature dependent resistivity of Pr(Fe, Co, Ni)4Sb12

model

with nar- row gap right abo- ve EF – metallic beha- viour at low temperatures – semiconducting- like behaviuour at high tempe- ratures – gap of the or- der of 0.1 eV

SLIDE 48

Thermopower - Seebeck coefficient

Sd = π2k2

BT

3|e| 1 N(EF) ∂N(E) ∂E

E=EF

T[K]

50 100 150 200 250 300

S [µV/K]

20

20 40 60 80 Pr0.73Fe4Sb12 Nd0.72Fe4Sb12 La0.83Fe4Sb12 Pr0.5Co4Sb10Sn2

Pr0.73Fe4Sb12 exhibits pro-

nounced minimum due to strong hybridisation effects;

hybridisation

absent in Pr0.5Co4Sb10Sn2; S(T) small!

isomorphous La- and Nd- sys-

tems show smaller

verall

S(T) values;

positive Seebeck coefficients

at high temperatures indica- te hole-dominated transport processes.

SLIDE 49

Kondo enhanced thermopower

SLIDE 50

Kondo enhanced thermopower

H. Sato et al, 2000

Sd = π2k2

BT

3|e| 1 N(EF) ∂N(E) ∂E

E=EF

⇒ Sd = 2π |e|N γ cot(πnf/N) = = 2π |e|N γ cot(ηf(0))

γ, Sommerfeld coefficient; nf, 4f occupancy; N, degeneracy of 4f state (N = 2j + 1).

correlation between γ value and

thermopower!

phase shift ηf: ±S(T) values.

SLIDE 51

Thermopower: relation to carrier concentration

SLIDE 52

Thermopower: relation to carrier concentration

Sd = π2k2

BT

3|e| 1 N(EF) ∂N(E) ∂E

E=EF

≈ π2k2

BT

3|e| 1 2EF (parabolic band) small EF values necessary ⇒ heavy fermion systems! stable filler element

reduction of carrier concen-

tration due to – substitution of Fe/Ni; – reduction of trivalent fil- ler element;

Fe/Ni substitution causes a

loss of hybridisation effects.

SLIDE 53

Thermal conductivity of Pr(Fe, Co, Ni)4Sb12

λ = λe + λph λe = LeT ρ ≈ L0T ρ L0 = 2.45 × 10−8 WΩ/K2; L0 . . . Lorenz number

overall

low thermal con- ductivity

filler atoms si-

gnificantly re- duce λ(T)

radiation losses

at high tempe- ratures in stea- dy state techni- ques

SLIDE 54

Thermal conductivity of Pr(Fe, Co, Ni)4Sb12

λ = λe + λph λe = LeT ρ ≈ L0T ρ L0 = 2.45 × 10−8 WΩ/K2; L0 . . . Lorenz number

overall

low thermal con- ductivity

filler atoms si-

gnificantly re- duce λ(T)

radiation losses

at high tempe- ratures in stea- dy state techni- ques

SLIDE 55

Thermal Conductivity: Analysis

SLIDE 56

Thermal Conductivity: Analysis

Debye approximation for lattice thermal conductivity: λph = CT 3 θD/T τcx4 exp(x) [exp(x) − 1]2dx x = ¯ hω/kBT, ω (phonon frequency), θD (Debye temperature); τc . . . overall relaxation time: τ −1

c

= τ −1

B + τ −1 D + τ −1 U

+ τ −1

e

τb, τD, τU, τe relaxation times for boundary scattering, defect scattering, Umklapp processes and electron scattering, respectively. τ −1

B

= B τ −1

D = Dω4

τ −1

U

= Uω2T exp(−θD/3T) τ −1

e

= Eω

SLIDE 57

Thermal conductivity of Pr(Fe, Co, Ni)4Sb12

SLIDE 58

Thermal conductivity of Pr(Fe, Co, Ni)4Sb12

filler atoms si-

gnificantly re- duce λ(T)

importance
f

phonons scattering

n

point defects; τ −1

D = Dω4

SLIDE 59

Thermal Conductivity of REFe4Sb12

SLIDE 60

Thermal Conductivity of REFe4Sb12

T [K]

100 200 300

λ [mW/cmK]

10 20 30 40 50

Pr0.73Fe4Sb12 La0.83Fe4Sb12 T [K]

20 40 60 80 100

λ [mW/cmK]

6 9 12 15

Pr0.73Fe4Sb12 La0.83Fe4Sb12 lattice thermal conductivity

electronic thermal conductivity

Lattice thermal conductivity

magnetic

interacti-

n: reduction λe and

λph (τph−el = Eω)

λe of Pr smaller than
f La!
phonon

interaction with quasi-particles, valence fluctuations, etc., possible sources for reduced λ

SLIDE 61

Thermal Conductivity of REFe4Sb12

T [K]

100 200 300

λ [mW/cmK]

10 20 30 40 50

Pr0.73Fe4Sb12 La0.83Fe4Sb12 T [K]

20 40 60 80 100

λ [mW/cmK]

6 9 12 15

Pr0.73Fe4Sb12 La0.83Fe4Sb12 lattice thermal conductivity

electronic thermal conductivity

Lattice thermal conductivity

magnetic

interacti-

n: reduction λe and

λph (τph−el = Eω)

λe of Pr smaller than
f La!
phonon

interaction with quasi-particles, valence fluctuations, etc., possible sources for reduced λ

SLIDE 62

Summary

large number of binary and ternary skutterudites

– filler element determines physical properties

rare earth as guest atom

– superconductivity, Kondo effect, heavy fermion behaviour, mixed - and intermediate valence, . . .

electronic transport depends in a subtle manner on charge

carrier concentration and on various interactions (electron correlation, crystal field splitting, . . . ) – electron - and hole - like transport

filled skutterudites are potential candidates for thermoelectric