NONLINEAR CONDUCTIVITY

OF QUASI-ONE-DIMENSIONAL LAYERED COMPOUND TiS3.

I. G. Gorlova, V. Ya. Pokrovskii, S. G. ZybtsevKotel’nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences,ul. Mokhovaya 11-7, Moscow, 125009 RussiaE-mail: gorl@cplire.ru

N. B. Bolotina, I. A. VerinShubnikov Institute of Crystallography of Russian Academy of Sciences,Leninskii pr. 59, Moscow, 119333 Russia

A. N. TitovInstitute of Metal Physics, Ural Branch of Russian Academy of Sciences, ul. S. Kovalevskoi 18, Yekaterinburg, 620131 Russia

Transition metal trichalcogenides of Group IV metals. MX3, where M =Ti, Zr, Hf; and X=S, Se, Te.

F.S. Khumalo and H.P. Hughes, PRB, 22, 2078 (1980)

Diamagnetic semiconductors with the exception of ZrTe3 and TiS3, which show metallic properties. ZrTe3 undergoes a phase transition at 63 K due to CDW formation.

The quasi-one-dimensional layered compound TiS3.

Pei-Ling Hsieh, C. M. Jackson, and G. Grüner Solid State Commun., 46, 505 (1983).

Unit cell parameters: a=0.50 nm, b=0.34 nm, c=0.88 nm.=98,4Structural type – monoclinicSpace group – P21/mS. K. Srivastava and B. N. Avasthi, J. of Materials Science, 27, 3693 (1992).

Resistivity in the direction along the chains: ρb(300 К) = 2.5 Ohm x cm.Pei-Ling Hsieh, C. M. Jackson, and G. Grüner Solid State Commun., 46, 505 (1983).

Electron density:n(300 К)~21018 cm-3. O. Gorochov, A. Katty, N. Le Nagard, C. Levy-Clement, and D. M. Schleich, Mater. Res. Bull. 18, 111 (1983).

60 K

The crystal structure and growth defects of TiS3 whiskers.Results obtained by transmission electron microscope HVEM JEM-1000.

a

b

a

b

The brightfield microphotograph of the TiS3 whisker. Dislocations are seen in the ab plane (a). A number (wall) of dislocations and growth steps are directed along the b axis (b).

The diffraction patterns of the same sample at 285 K (a) and at 155 K (b).

a*

b*

a

b

Electrical contacts to TiS3 whiskers .

Contact resistance at 300 K was ~ 10-6 Ohm x cm2.

100µm 100 µm

The TiS3 whisker with 4 indium contacts prepared for longitudinal measurements. The measuring current flows along the chains (along b axis).

The TiS3 whisker with four gold contacts prepared for transverse measurements. The measuring current flows across the chains (along a axis).

b a

II

The ab-plane anisotropy of conductivity of TiS3.

The temperature dependences of the resistance of TiS3 in the longitudinal (R||) and transverse (R) directions normalized by the values at T = 300 K. The arrows mark the temperatures 120, 59 and 17 K at which the maxima of dlnR/d(1/T) are observed. The inset shows the temperature dependence of the ratio ρ/ρ|| Resistivity in the b direction at room temperature is: ρb(300 К) 2 Ohm x cm. ρa/ρb ~ 5 at 300 K. ρa/ρb ~ 100 at 75 K. b~ 1.5 cm2/Vxs, a~ 0.3 cm2/Vxs

The temperature dependences of the logarithmic derivatives dlnR/d(1/T).

Differential resistance, Rd, of TiS3 whiskers versus the applied voltage.

Rd, measured along b-axis vs. Vat T = 4.2, 4.4, 4.7, 5.2, 6.1, 7, 8.5, 9.7, 10.6, 11.8, 13, 14, 15.7, 18, 21.9, 27, 32.1, 37, 45, 50, 55, 60, 70, 80, 90 K.

Rd, measured along a-axis vs. V

at T = 4.2, 10, 14, 17, 21, 31, 41, 55, 65, 80, 95, 110, 125, 140 K

Differential resistance, Rd, of TiS3 whiskers versus the applied voltage.

Rd, measured along b-axis vs. V

at T =10, 15, 20, 30, 35, 40, 45, 50, 55, 60, 65 K. Rd, measured along a-axis vs. V at T = 4.2, 10, 14, 17, 21, 31, 41, 55, 65, 80, 95, 110, 125, 140 K

Nonlinear b and a conductivities of TiS3 whiskers at equal E values.

Temperature dependences of the linear conductivity σ(0) measured at the current I ≤ 0.1 μA (thick lines) and the nonlinear part of differential conductivity σn = σd(V) – σd(0) at the specified voltages mentioned at the corresponding curves (circles) . Thin solid lines are guides for eye. Notice that σb(0) is divided by 100 and σa(0) is divided by 30.

Longitudinal σ ( measured along b axis).

The sample length is 56 µm.

Transverse σ ( measured along a axis).

The sample length is 30 µm.

TiS3 and Paierls conductors.

• Common features:

1. Quasi-one-dimensional structure.

2. Maxima of the dlnR/d(1/T) derivative of the temperature dependence of the resistivity for both longitudinal and transverse directions at the transition temperatures.

3. Increase in the ab-plane anisotropy of the conductivity with a decrease in the temperature. The anomaly in the ratio ρ/ρ|| at the transition temperature.

4. Onset of the electric field dependence of the resistance at the temperatures at which the maxima of the derivative dlnR/d(1/T) are observed.

5. The temperature dependence of the nonlinear conductivity has features at the same temperatures as the linear conductivity.

6. Weak temperature and electric field dependences of nonlinear conductivity in high electric fields.

• Distinguishing features:

1. The resistivity of TiS3 is ρ3002 Ohmxcm, i.e. 3-4 orders of magnitude higher than that of known conductors with the charge density wave.

2. The electron density in TiS3 at room temperature determined from the Hall effect is n~21018 см-3. To date, the Peierls transition was observed only in quasi-one-dimensional conductors with a relatively high carrier density (n~21021 см-

3 at T = 300 K).

3. The anisotropy of the conductivity of TiS3 in the ab plane is comparatively small ρa/ρb5 at 300 K (3 times smaller than that of NbSe3 and 30 times smaller than that of TaS3).

4. The zero-voltage peaks instead of the threshold behavior of the current–voltage characteristics.

5. Nonlinear transverse conductivity (along the a-axis) at T<120 K.

h00 scan at T=250 KX-ray study of TiS3 whiskers at different temperatures.

Scans along a-axis.

h00 scan at T=200 K

h00 scan at T=55 K

Shubnikov Institute of Crystallography of RAS

Low-temperature four-circle diffractometer Huber 5042

Mo-anode

Power-law behavior of resistance in TiS3 whiskers.

Variable-range hopping in quasi-1D systems: R T-α, R V-

For LL: α = 2

A.S. Rodin, M.M. Fogler PRL 105, 106801 (2010)

α = 1

T = 4.2, 10, 14, 17, 21, 31, 41, 55, 65, 80, 95, 110, 125, 140 K

4.2 K

140 K

Wigner crystal type of charge ordering, in the quasi-one-dimensional organic conductors (DI-DCNQI)2Ag и (TMTTF)2PF6

F. Nad, P. Monceau, C. Carcel, and J. M. Fabre,PRB 62, 1753 (2000)

CONCLUSIONS

• The crystal structure and transport properties of TiS3 whiskers in the plane of layers (ab) have been studied.

• Maxima of the logarithmic derivative of resistance are observed at 17, 60 and 120 K both along and across the chains.

• Strong nonlinearity of the current–voltage characteristics has been revealed in both directions. Nonlinear conductivity along the chains is observed up to T=60 K. In the transverse direction it is observed up to T=120 K.

• The results indicate possible phase transitions of electrons to collective states, probably, charge density waves.