ECRYS 2011

Anomalous behavior of ultrasonic

properties near 50K in A0.30MoO3

(A=K, Rb) and Rb0.30(Mo1-xVx)O3

M. Saint-Paul, J. Dumas, J. MarcusInstitut Néel, CNRS/UJF, Grenoble, France

Outline

1. Anomalies at ~50K in the CDW conductor K0.30MoO3

2. Ultrasonic properties of Rb0.30MoO3, K0.30MoO3

Velocities of longitudinal modes

Ultrasonic Attenuation

Role of disorder : Rb0.30Mo1-xVxO3

3. CDW glassy behavior

4. Conclusion

J.P. Pouget et al.

K0.30MoO3 Quasi-1D conductor; Tp = 180K

Chains along b (a,c) plane

Nonlinear conductivity at low temperature

• Large and abrupt threshold field at low T.• Very low damping due to freezing of

normal carriers

• T < 50K• Rigid CDW in the low temperature• Insulating state

• G.X. Tessema, L. Mihaly, (1987)• G. Mihaly, P. Beauchêne et al., (1988)

G. Mihaly, P. Beauchêne

Temperature dependence of the threshold fields Et1, Et2

Two different regimes: T > 50K : Et1 ≈ 0.1V/cm: Strong damping T < 50K : Et2 ≈10 V/cm: Low damping

P. Beauchêne, G. Mihaly et al. (1988); J. Dumas, C. Schlenker (1993).

H. Li, J. Wang et al., Mod. Phys. Lett. B 18, 697 (2004).

Tp

T>50K:Deformable CDW

T<50K: Rigid CDW

Proton channeling at low temperature

Proton Beam perpendicular to cleavage plane:

Backscattering yield Xmin increases below 40K.

No effect for beam // [102] direction and perp. b

(in the cleavage plane)

Structural Disorder at low T.

CDW defects

B. Daudin, J. Dumas et al., Synth. Metals (1989)

Mingliang Tian et al. Phys. Rev. B (2000)

Lattice parameters

T(K)

Noticeable change T ~ 50K

Interlayer distance d [-201]

chain axis

-0.5

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250T (K)

[102]

Tp

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 20 40 60 80 100

L/L

4K (

10-3

)

T (K)

Normalized thermal expansion

along [102] along the transverse direction [-201]

L/L4K <0 below 50K L/L4K [-201] larger than that along the layers [102]

G. Remenyi, J. Dumas (2009)

-Change in phason behaviour near 40K: S. Ravy et al., Phys. Rev. B (2004)

J. Dumas, B. Layadi et al. Phys. Rev. B (1989)

Ratio of the Mo5+ (S=1/2) EPR lines intensities:

slow cooling / fast cooling

Role of the cooling rate: Rapid change of relative EPR intensities near 50K.

No effect on V-doped samples

probe the CDW state through interaction between the defects and the CDW modulation

Measuring Temperature

D. Staresinic et al. Phys. Rev. B (2004)

Dielectric spectroscopy

Glassy behavior for

the CDW

at low temperature

50K

Relative change of the velocity of the longitudinal modes (15MHz) propagating along b, [102], [-201] directions

Large increase of the velocity below ~50K in the three directions.

Pronounced softening at Tp along [102].

Pronounced stiffening below ~50K.

//b

Platelets 5x4x2mm3

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 50 100 150 200 250

TP

T (K)

[010]

[102]

[-201]

Rb0.3

MoO3

V = (C/

-0.04

-0.03

-0.02

-0.01

0

0.01

-5

0

5

10

15

0 20 40 60 80 100

[102]

T (K)

(a)

(b)

Velocity of the longitudinal mode along [102] and attenuation

Anharmonic contribution

Attenuation :

Additional contribution T<50K Disorder in CDW superlattice

TV

TC

V

V2

0

2

2

)(

2

2

)(1

)(

2

)(

R

Ru

V

VV

V

V

2

2

2 )(1

)(

4

1

R

Ru

V

VV

Arrhenius law:

= 0exp(325/T) 0 =10 -11 s

V/V = -AT

Linear term T<20K: V/V= -AT. « Bellessa effect », common feature of glasses.

A

Bellessa effect V/V = - AT

Amorphous and disordered materials; Bellessa et al. PRL (1978); Nava et al. PRB (1994).

( , ) our results

Nava et al.

-0.04

-0.03

-0.02

-0.01

0

0.01

0

1

2

3

4

5

6

7

0 20 40 60 80 100

T (K)

[-201]

Longitudinal mode along the transverse direction [-201]

Anharmonic contribution

= 0 exp(325/T)0 =10 -11 ssame activation energy

Ea=325K : low temperature -relaxational process in dielectric measurements

(D. Staresinic et al.)

-0.015

-0.01

-0.005

0

0.005

0.01

-5

0

5

10

15

20

10 20 30 40 50 60 70T (K)

15MHz

1MHz

15MHz

1MHz

[102] Relative change in velocity and Plateau in the attenuation shifted to lower T when the frequency is decreased.

Velocity of the longitudinal mode along [102] at 15MHz and 1MHz

Frequency dependent anomaly

Ea = 325K at 15 MHz

Ea = 360K at 1MHz

K0.30MoO3:

Relative change of the sound velocity : Longitudinal mode along [-201]

Similar activated behavior near 50K.

Ea= 325K

-0.02

-0.015

-0.01

-0.005

0

0.005

0

5

10

15

0 50 100 150 200

T (K)

K0.3

MoO3

[-201]

The alkaline element K/Rb plays no important role in the anomaly.

J. De Boer (100K)

K Rb

A (Å) 18.162 18.536

b 7.554 7.556

c 9.816 10.035

117.3 118.5

-0.015

-0.01

-0.005

0

0.005

0.01

0 20 40 60 80 100

T (K)

[102]

(a)

(b)

Role of disorder : Rb0.30 (Mo1-x Vx) O3 x = 0.4 at %Relative change of the velocity of the longitudinal mode propagating along [102] direction.

● V, non isoelectronic impurity; substitution V5+ / Mo6+. Strong pinning centers. Short range CDW order.

S. Ravy et al., Phys. Rev. B (2006).

Smearing out of the anomaly and shift towards higher temperature ~70K

V/V=-AT

Anharmonic contribution

Ea ~ 500K

15 MHz

-0.01

-0.005

0

0.005

0 20 40 60 80 100T (K)

(a)

(b)

Ea=500K

Ea= 330K

[-201]

Rb0.30 (Mo1-x Vx)O3 x = 0.4 at % along the transverse direction [-201]

Smearing out of the anomaly and shift towards higher temperature.

Smaller size of domains of coherence of the CDW.

Vogel-Fulcher empirical law : = 0exp[ U/(T-T0 ] ; T>T0

glass - like behaviour

Average activation energy U = 220K

Freezing temperature

T0 = 16K

our results

Thermoelectric power , Kriza et al.

() K. Biljakovic

et al.

Dynamic effect rather than thermodynamic phase transition

= 1

Vogel-Fulcher law

Rb0.3MoO3 Longitudinal sound velocities and elastic constants

T=300K

Along b 5300m/s C22 = 1.2x1011 N/m2

Along [102] 4800 m/s C// = 1011

Along [-201] 3300m/s C = 4.6x1010

Velocities comparable to those of K0.3MoO3

M. Saint-Paul, G.X. Tessema (1989)

Water: 1480m/s ; Pb: 1960m/s; Cu: 5010m/s

Conclusions

-Large elastic anomalies at T~50K along b, [102], [-201] :

-Stiffening of longitudinal waves T<50K, along b, [102], [-201]

-Linear term T<30K

-Increase of the attenuation T ~ 50K followed by a plateau

-Anomaly in Rb0.30 Mo1-xVxO3 shifted towards higher temp.

-Dynamic effect rather than thermodynamic transition

-Consistent with CDW glassy-like state

-0.5

0

0.5

1

1.5

2

2.5

3

0 50 100 150 200 250T (K)

[102]

Tp

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 20 40 60 80 100

L/L

4K (

10-3

)

T (K)

Normalized thermal expansion along [102]

L/L4K < 0 below ~ 50K

Normalized thermal expansion along the

transverse direction [-201]

L/L4K

two times larger than that along the layers [102].

L/L4K < 0 below ~50K.

Anharmonic phonon dynamics.

n < 0 for some low energy modes

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

0 50 100 150 200 250

T (K)

[102]

Thermal expansion coefficient along [102]

-0.02

-0.01

0

0.01

0.02

0.03

0 25 50 75 100

V/V

T (K)

Attenuation Shear mode W

ave

Am

pli

tud

e

Echogram

[-201]

Large attenuation on the plateau

Thermal history : Shear mode along [-201], transverse direction

-0.02

-0.01

0

0.01

0.02

0.03

0 25 50 75 100

T (K)

[-201]

smectic nematic

atte

nu

atio

n

Analogy with smectic - nematic transition ?

F. Kiry, P. Martinoty, J. Phys. 1978

Magnetic susceptibility

B.T. Collins, K.V. Ramanujachary, M. Greenblatt,

Solid State Comm. 56, 1023 (1985).

Tl0.3MoO3 K0.3MoO3

L.F. Schneemeyer, F.J. DiSalvo, R.M. Fleming, J.V. Waszczak, J. Solid State Chem. 54, 358 (1984)

Order Parameter

J.P. Pouget et al. (1985)

Thermally stimulated depolarization current

R.J. Cava, R.M. Fleming et al., Phys. Rev. Lett (1984).

F.Nad et al., ECRY93. J. Phys. IV C2, Vol.3, 343 (1993).

J. Yang, N.P. Ong, Phys. Rev. B (1991)

B. Zawilski et al. Solid State Comm. 124, 395 (2002)