Poole Ch.P., Jr. Handbook of Superconductivity

96 Chapter 5: Superconductor Types

Table 5.26.

AX4P12 phosphide compound,

LaFe4P12 (skutterudite), ci34.

X 4 =~ Fe Ru

A 8 8

La 3 4.1 7.2

Ce 3 <0.35 <0.35

Pr 3 <0.35 <0.35

Nd 3 < 1.0 < 1.0

H

Fullerenes

Arthur

P. Ramirez

The C60 molecule sketched in Fig. 6.26 was originally discovered in molecular

beam experiments. It is one of the most stable molecules in the series of even-

numbered fullerenes and the one that most closely approximates a sphere. C60 is a

truncated icosahedron, that is, a polygon with 60 vertices and 32 faces divided

into 20 hexagons and 12 pentagons. The solidification of C60 is a multistep

process. First, soot is formed by spark erosion in a helium atmosphere. Second,

column chromatography is performed to isolate the C60 components of the soot.

Then, for single crystal production, the black powder is dissolved in a nonpolar

solvent such as benzene, which is then allowed to evaporate, leaving behind small

(<1 mm) single crystals. For both powder and crystalline samples doping is

achieved by exposing C60 to alkali vapor in the absence of air.

Solid C60 is the third crystalline form of carbon, besides diamond and

graphite. The crystal structure is fcc. The diameter of a C60 molecule is 7 A and C

atoms are separated by 1.4-1.45 A, depending on whether the bonds comprise a

pentagon or connect pentagons. The separation between the C60 molecules on the

edge of the fcc cell is 14.2 A for pure C60 and increases to 14.25 A for K 3 C60 and

to 14.43 A for Rb3C60. There are other structural variations among doped C60

compounds: A2C60 is fcc, A4C60

is bct, and

A6C60 is bcc,

where A is an alkali

atom. None of these compounds exhibit superconductivity, at least not above 2 K.

Other compound families can be formed by intercalating NH 3 and alkaline earths.

All of these systems are nearly line compounds at room temperature, meaning

that continuous doping is not possible.

Undoped, C60 is a semiconductor with a band gap of about 1.5 eV. Because

of the curvature of the molecular surface, there is a significant ~-p hybridization,

intermediate between that of diamond and graphite. The band widths are typically

0.5 eV and are identified by the parent molecular orbitals. The extra rotational

H. Fullerenes 97

Table 5.27.

AxMo6X8 compound, for X = S, Se and 0 < x < 2, PbMo6S 8 type (Chevrel), hR45. Columns 2 and 3

are for x- 1, columns 4 and 5 are for x = 1.2, and the remaining columns are for special cases.

T12Fe6Te 6 type hP14 Chevrel compounds are marked with the asterisk (*).

Case x = 1.0 Case x = 1.2 Special cases

X 8 =~ S Se S Se

A 6 6 6 6 Compound T c

Li 1 5.5 3.9

Na 1 8.6

K 1 2.9

Ag 1 9.5

Ca 2 6.0

Hg 2 8.1

Sc 3 3.6

Y 3 6.2 2.1

In 3 <0.6 8.1

T1 3 8.7 12.2

La 3 7.0 11.4

Ce 3 <1.1 <1.1

Pr 3 2.6 9.2

Nd 3 3.5 8.2

Sm 3 2.4

Eu 3 <1.1

Gd 3 1.4

Tb 3 1.4

Dy 3 1.7

Ho 3 1.9 2.0

Er 3 <1.1 2.0

Tm 3 2.0

Yb 3 8.6 5.8 8.7

Lu 3 2.0

Np 3 5.6

Pu 3 <2.5

Am 3 <3.5

Sn 4 11.8 14.2

Pb 4 15.0 3.8

Sb 5 <2

Bi 5 <2

5.9

6.8

<1.1

5.6

5.7

5.8

6.1

6.2

6.3

5.8

6.2

Mo6S 8 1.9

Mo6Se 8 6.5

Mo6Se6* <1

Mo6Se8* <1

Mo6Te 8 1.7

BrMo 6 Se 7 7.1

Br2Mo6S 6 13.8

IMo6Se 7 7.6

IzMo6S 6 14.0

IzMo6Te 6 2.6

CuzMo6S 8 10.7

CUl.73Mo688 a 10.9

Cu2Mo6Se 8 5.9

ZnzMo6S 8 3.6

CdMo5S 6 3.5

InzMo 6 Se 6. < 1

In 2 Mo 6 Te 6 * < 1

TlzMo6Se6* 5.8

TlzMo6Te6 * <1

* T12Fe6Te 6 type hP14 structure.

a

hR78 structure.

98

Chapter S: Superconductor Types

Table 5.28.

A2B3Si 5 silica compound, U2Mn3Si 5 type

tP40 (no symbol) and U2Co3Si 5 type, o140

(designated by asterisk*).

B 3 =:~ Re Fe Rh Ir

A 2 7 8 9 9

Sc 3

Y3

La 3

Lu 3

Tm 3

4.5

1.8 2.4 2.7* 3.0*

4.4*

6.1

1.3

Table 5.29.

A3X4Y13 compound, Yb3Rh4Snl3 type, cP40; stannides A3X4Snl3 are on the left, and germanides

A 3 X 4 Gel3 are on the right.

A3X4Snl3 compounds A3X4Gel3 compounds

X 4 :=~

Ru Os Rh Ir Co Ru Os Rh Ir Co

A 3 8 8 9 9 9 8 8 9 9 9

Ca 2 8.7 7.1

Sr 2 4.3 5.1

Sc 3 4.5 1.1

Y 3 3.2

La 3 3.9 3.2 2.6 2.8

Lu 3 3.2

Th 3 5.6 1.9 2.6

Yb 3 8.6 2.5

5.9 2.1 1.7

1.7 3.9

2.3 3.6 2.3

1.9 1.4

T c = 4.8 K for La3RuPd3Sn13 and Tc = 2.2 K for La3Rh4Pbl3 , both with structure cP40; T~ = 3.2 K

for La3Rh4Snl3, with structure ci320.

Table

5.30.

A4XsY10 compounds, Sc5Co4Si10 type, tP38; silicides A4XsSil0 are

shown on the left and germanides AaX5Gel0 on the right.

A4XsSil0 compounds

A4XsGel0 compounds

X 5 =, Sc Y Lu X 5 =, Sc Y Lu

A 4 3 3 3 A 4 3 3 3

Co 9

Rh9

Ir 9

4.7 Os 8 9.1

8.4 4.0 Rh 9 1.4 2.8

8.4 3.1 3.9 Ir 9 2.7 2.6

H. Fullerenes 99

Table 5.31.

A4X6Snl9 compound with

two structures,

Tb4Rh6Snl9 type, cF116

(no

symbol) and

Er4Rh6Snl9 type, ti232 (designated by *).

X 6 ==} Ru Os Co Rh Ir

A 4

8 8 9 9 9

Sc 3 1.5

Y 3 1.3 2.5

Lu 3 <1.1" 1.8

Tb 3 1.4

Ho 3 1.4

Er 3 <1.1" 1.3

Tm 3

1.1

1.5*

4.5* 1.1"

3.2* 2.2

4.0* 3.2*

<1.1" 1.2" <1.1"

2.3* <1.1"

Ca4Rh6Pbl9 3.3*; Sc4Ir6Gel9 1.4"; Sc4Rh6Gel9 1.9".

degree of freedom of the

C60

molecule gives rise to unusual structural behavior in

the undoped material. This behavior includes orientational ordering at 260 K and

glassy dynamics observed below 200 K in thermal conductivity, dielelectric

constant, and Young's modulus studies. This behavior is not observed in the

doped compounds, and it is also not clear to what extent residual rotational

Table

5.32.

A nMO15 Se19 compound with

two structures:

~-MolsSel9 type, hP68 (no

symbol) and

fl-Mo15Se19

type, hR204 (designated by an asterisk *).

A~ N e Tr (K)

Li 2 1 2.6*

Li 3 1 3.5

Na 2 1 <0.5*

Na 3 1 <0.5

K2 1 2.1"

Cd2. 5 2 <0.5*

In 2 3 1.4"

In 3 3 3.8

Sn 2 4 <0.5*

In 2 3 <0.5*

K2In 1.7 1.3

For hP68 structure

T c <0.5K for X=S

and

A~ = Na, K, Zn, Cd, In, T1, Sn, Pb; T c < 0.5 K

for

MolsS19 and T c = 4.3 K for MOlsSel9.

For hR204 structure,

T c = 4.3 K for MOlsSel9 ,

and

T c = 3.3 K for K2Mo15S19.

I00

Chapter 5: Superconductor Types

Table 5.33.

Miscellaneous AmBnC p and AmBnCpD q compounds with various

structures.

Compound Tc(K ) Structure

ABC

ABC2

ABC 3

AsHfOs 3.2 hP9

AsHfRu 4.9 hP9

AsOsZr 8.0 hP9

AsRuZr 11.9 hP9

GelrLa 1.6 tI12

GeLaPt 3.5 tI12

HflrSi 3.5 oP 12

HfOsP 6.1 hP9

HfPRu 10.0 hP9

IrSiTh 6.5 tI12

IrSiTi <1.7 oP12

IrS iY 2.7 o P 12

IrSiZr 2.0 oP12

LaPtSi 3.3 tI12

LaRhSi 4.4 cP 12

NbPRh 4.4 oP12

NbPS 12.5 oi12

NbReSi 5.1 oi36

NbRuSi 2.7 o136

OsPTi 1.2 hP9

OsPZr 7.4 hP9

PRhTa 4.4 oP12

PRhZr 1.6 oP12

PRuTi 1.3 hP9

PRuZr 3.7, 12.9 oP12, hP12

ReSiTa 4.4 o136

RuSiTa 3.2 o136

BCMo 2 7.5 oS 16

BNNb 2 2.5 oS 16

BiPbPt2 1.3

BiSbNi 2 2.0 hP

BiSbPt 2 1.5 hP

IrLaSi 2 2.0 oS 16

LaRhSi 2 3.4 oS 16

LaRuB 2 7.8 oP 16

NiRhBi 2 3.0 hP

PdPtBi 2 3.7 hP

ReWC 2 3.8 oF8

CIrMo 3 3.2 cF

IrLaSi 3 2.7 tI10

LaRhSi 3 2.7 tI10

H. Fullerenes 101

AB2C 2

AB2C3

AB2C4

AB3C3

Table 5.33.

Compound

(continued)

Tc(K)

Structure

MoReC 3

TaPbS 3

ThlrSi 3

ThRhSi 3

LaB2C 2

LaRhzSi 2

LaRu2P 2

LuB2C 2

SrRu2P 2

ThlUr2Si 2

UAlzGe z

yBzC2

YIrzSi 2

YRhzSi 2

3.8

3.0

1.8

<1.8

3.9

4.1

2.4

<1.8

2.1

1.6

3.6

2.6

3.1

cF8

tI10

tPl0

tI10

tPl0

tI10

cP

tP10

tI10

CA12Mo 3

CIr2W 3

CIr2Mo 3

COs2W 3

CPt2Mo 3

CPt2W 3

LaB2Rh 3

LaB2Ir 3

LaSi2Ru 3

LuB2Os 3

OsY2Ir 3

ThB2Ir 3

ThB2Ru 3

ThSi2Ru 3

YB2Ru 3

YSi2Ru 3

10.0

2.1

1.8

2.9

1.1

1.2

2.8

1.7

7.6

4.6

2.4

2.1

1.8

4.0

2.9

3.5

cP24

cF

hP6

hP12

hP6

hP

hP6

hP12

hP6

hP12

CuRh2 S 4

CrRh2 Se 4

CHV2S 4

HfP2Ru 4

ZrP2Ni 4

ZrP2Ru 4

4.4

3.5

4.5

9.5

<2.0

11.0

cF56

tP14

OV3Zr 3

T1Mo3Se 3

T1Os3W 3

7.5

4.0

2.1

cFll2

hP14

102 Chapter 5: Superconductor Types

AB3C 4

AB3C9

AB4C12

A2B3C5

A2BsC6

A2B6C9

A3B4C13

AmBnCpDq

Table S.33.

(continued)

Compound Tc(K )

Structure

NiPd3As 4 1.6 hP

SbTe3In 4 1.5 cF8

SeTe3Nb 4 4.4

NaW200 3.0

LaFe4P12 4.1 ci34

LaRu4P12 7.2 ci34

La2Rh3 Si 5 4.5 o140

Y2Ir3Si5 2.8 o140

Y2Rh3Si5 2.7 o140

B2La5C 6 6.9 tP52

Bao.67 B 2 Pt 3 5.6 hP 12

Cao.67B 2 Pt 3 1.6 hP 12

Sro.67B2Pt 3 2.8 hP12

La3Rh4Snl3 3.2 ci320

BNLaNi <4.2 tP8

B2Ni2N2.9La 3 13.0 tI20

B2BrsC6La 9 6.6 oP46

motion hinders superconductivity. The energy scale for rotational motion is much

lower than that needed to produce the large T c's observed.

The superconducting phase has a stoichiometry of three alkali atoms for

each C60 molecule. The mechanism of doping involves charge transfer from the

alkali-atom outer shell onto the C60 molecule, populating the

tau

molecular

conduction band. The alkali atoms do not possess states near the Fermi level and

are thus electronically inactive. The highest reported T c is 40 K for Cs3C60,

although this material is metastable. The more stable forms K3C60 (T c -- 19.5 K)

and Rb3C60 (T c = 29.5 K) have properties listed in Tables 5.38 to 5.40. Ramirez

(1994) has reviewed superconducting fullerenes.

H. Fullerenes

103

Table 5.34.

AB magnet material alloys, A(BxCx_x)O 3 tetragonal and cubic

perovskites, and AB2X 4 spinels.

Type Compound T c Structure

Magnet alloy

Perovskite

Spinel

Nb-Ti, 50 mole %Nb 9.5

Nb-Ti, 67 mole %Nb 10.1

Nb-N 1 O.5

Nb3Sn, A15 compound 17.9

cP8

BaPb0.8Bi0203, tetragonal 10.0 tI20

BaPb0.7Bi0. 3 03, tetragonal 11.5 tI20

Ba0.57K0.43 BiO3, cubic 30.0 cP5

Li0.75Ti204 13.2 cF56

Li 1.03 Ti1.90

04

12.3 cF 56

CuV2S 4 4.5 cF56

CuRh2S 4 4.4 cF56

CuRh2Se 4 3.5 cF56

Table 5.35.

Properties of several heavy electron superconductors where T c is the

superconducting transition temperature, T N is the Nrel temperature, |

is the Debye temperature, /2ef f is the effective magnetic moment, and

m*/m e

is the ratio of the effective mass to the free electron mass.

Compound

Tc(K )

TN(K ) OD(K ) ]2eff/]2 B

m*/m e

NpBel3 3.4 -42 2.76

UBe13 0.85 8.8 -70 3.1 192

UCdll 5.0 -23 3.45

UPt 3 0.43 5.0 -200 2.9 187

U2Znl7 9.7 -250 4.5

CeCu2 Si 2 0.6 0.7 - 140 2.6 220

Most of the data on the superconducting phase can be understood using

existing strong coupling (McMillan) theory. The magnitude of T c, which is

greatest among noncuprate materials, can be understood as arising from the

combined effects of (1) a large phonon frequency arising from intramolecular

modes; (2) a strong electron-phonon coupling resulting from the curvature of the

molecular surface, which leads to strong

sp 2

hybridization among the n-orbitals

of neighboring carbon atoms; and (3) a large density of states arising from the

narrow bands, which is a direct result of the spatial separation between C60

molecules.

104 Chapter S: Superconductor Types

Table

5.36.

Properties of superconducting borocarbides RNi2B2C , where R = Gd-Lu, Y.

T c Bc2(2 K) T N 0 c 0ab

0ave

lAeff Easy axis

(K) (kG) (K) (K) (K) (K) (lAB) (T-~ TN)

Gd <1.8 -- 20, 14 -- -1 8.1 iso

Tb <0.3 14.8 -60 16 0 9.8 100

Dy 6.2 4 B II e 10.3 -82 25 1 9.8 110

Ho 8.7 5

Bile

6, 5.5 -33 8.5 -1 10.4 110

5.0

Er 10.5 15 B II c 6.0 -6 -7.5 -7.0 9.4 100

Tm 11.0 18 B _1_ c 1.5 21 -36 -12 7.5 001

Yb <0.3 -- <0.3 -63 -191 -130 4.7 001

Lu 16.1 70

Y 15.6 90

0 and IAB values are taken from anlaysis of low field

M(T)

data using the Curie-Weiss form

M(T)/B = z(T) = C/(T - 0),

where C =

NlA2ff/3kB .

0 c and 0ab values are from

z(T)

data measured

with B

II

c and B A_ c, respectively.

0av e

and lAB are taken from a polycrystalline average of the z(T)

data Zave

= (Xc q-

2Zab)/3.

Table 5.37.

Transition temperatures of AX2B2C borocarbide compounds, LuNi2B2C type, tI12.

X 2 =:~

Rh Ir Ni Pd Pt Ptl.sAu0. 6

A 9 9 10 10 10 10.3

Sc 3

Sco.sLuo. 5 3

Y3

La 3

Lao.sLuo. 5 3

Lu 3

Lao. 5Tho. 5 3

Th 3

Pr 3

U3

Gd 3

Tb3

Dy 3

Ho 3

Er 3

Tm 3

Yb3

15.6

15.6 23.0 10.0 11.0

<4.2 <4.2 <4.2 10.0 11.0

14.8

16.1

3.9

8.0 14.5 6.5

6.0

<2.0

<1.8

<0.3

6.2

8.7

10.5

11.0

<0.3

6.5

I. Charge Transfer Organics 105

Table 5.38.

Solid-state parameters of two alkali metal doped fullerenes.

K3 C60 Rb3 C60

Lattice properties

fcc lattice constant a 0 (10 K) 14.25 A 14.43 A

Density 1.97 g/cm 3 2.23 g/cm 3

Phonon spectrum--average frequencies

Librational mode 4 meV

Intermolecular

modes

radial 25-110 meV

tangential 110-200 meV

Bulk modulus (undoped C60 ) 18.2 GPa

Bulk modulus (A3C60) 27 4- 1.9 GPa 21.9 + 1.9 GPa

Electronic parameters

n (electron density at 10 K) 4.24 x 1021 cm -3 4.1 x 1021 cm -3

% 1.56

eV

--

v F

= (zt4/3)l/3k2nZ/3]fh

1.4 x 107 cm/sec --

P0 (transport--films) ~2 m.Qcm

P0 (optical) ~0.4 m-Qcm

P0 (optical) 0.8 m,Qcm

P0 (mocrowave) 0.41 m,Qcm

P0 (specific heat, Hc2 ) 0.5 m.Qcm

N(Ev)

(thermopower) 14.2 4- 1.1 23.2 4- 0.7

N(E v)(NMR)

14.1 4- 1 23 -1- 1

N(Ev)(ESR) 10.6 4- 3

N(Ev)

(Zdc) 14 4- 1 19 4- 0.6

Charge Transfer Organics

The great majority of organic compounds and polymers are electrical insulators,

but a few of them do conduct electricity, such as salts of the compound

bis(ethylenedithio)tetrathiafulvalene, which is often called BEDT-TFE Figure

5.4 gives the structural formulas of this and other organic molecules that play the

role of electron donors in conducting and superconducting organics (Ishiguro and

Yamaji, 1990). The electrical properties of organic conductors are often highly

anisotropic and can exhibit low dimensional behavior. Crystallographic data and

transition temperatures of some of these compounds are given at the end of

Chapter 6.

Poole Ch.P., Jr. Handbook of Superconductivity

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