NONLINEAR CONDUCTIVITY OF QUASI-ONE-DIMENSIONAL LAYERED COMPOUND TiS 3 .

1. NONLINEAR CONDUCTIVITY OF QUASI-ONE-DIMENSIONAL LAYERED COMPOUND TiS3. I. G. Gorlova, V. Ya. Pokrovskii, S. G. Zybtsev Kotel’nikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, ul. Mokhovaya 11-7, Moscow, 125009 Russia E-mail: gorl@cplire.ru N. B. Bolotina, I. A. Verin Shubnikov Institute of Crystallography of Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia A. N. Titov Institute of Metal Physics, Ural Branch of Russian Academy of Sciences, ul. S. Kovalevskoi 18, Yekaterinburg, 620131 Russia

2. 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 andTiS3, which show metallic properties. ZrTe3 undergoes a phase transition at 63 K due to CDW formation.

3. The quasi-one-dimensional layeredcompound TiS3. Unit cell parameters: a=0.50 nm, b=0.34 nm, c=0.88 nm. =98,4 Structural type – monoclinic Space group – P21/m S. 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 xcm. Pei-Ling Hsieh, C. M. Jackson, and G. GrünerSolid State Commun., 46, 505 (1983). Electron density: n(300 К)~21018 cm-3. O. Gorochov, A. Katty, N. Le Nagard, C. Levy-Clement, and D. M. Schleich, Mater. Res. Bull. 18, 111 (1983). 60 K Pei-Ling Hsieh, C. M. Jackson, and G. Grüner Solid State Commun., 46, 505 (1983).

4. The crystal structure and growth defects of TiS3 whiskers.Results obtained by transmission electron microscope HVEM JEM-1000. a a* b b* a a b b The brightfield microphotograph of the TiS3whisker. Dislocations are seen in the abplane (a). A number(wall) of dislocations and growthsteps are directed along the b axis (b). The diffraction patterns of the same sample at 285 K (a) and at 155 K (b).

5. Electrical contacts to TiS3 whiskers .Contact resistance at 300 K was ~ 10-6Ohm xcm2. a b 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).

6. Theab-plane anisotropy of conductivity of TiS3. The temperature dependences of the resistanceof TiS3 in the longitudinal(R||) and transverse(R) directions normalized by the values at T =300 K. The arrows markthe temperatures 120, 59 and 17 K at which the maxima ofdlnR/d(1/T)areobserved. The inset shows the temperature dependence of the ratioρ/ρ|| Resistivity in the b direction at room temperature is: ρb(300 К) 2 Ohmxcm. ρa/ρb~ 5 at 300 K.ρa/ρb~ 100 at75 K.b~ 1.5 cm2/Vxs, a~ 0.3 cm2/Vxs The temperature dependences ofthe logarithmic derivativesdlnR/d(1/T).  II

7. Differential resistance,Rd, of TiS3 whiskers versusthe applied voltage. Rd, measured alongb-axisvs. V at 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 alonga-axisvs. V at T = 4.2, 10, 14, 17, 21, 31, 41, 55, 65, 80, 95, 110, 125, 140 K

8. Differential resistance,Rd, of TiS3 whiskers versusthe applied voltage. Rd, measured alongb-axisvs. V at T =10, 15, 20, 30, 35, 40, 45, 50, 55, 60, 65 K. Rd, measured alonga-axisvs. V at T = 4.2, 10, 14, 17, 21, 31, 41, 55, 65, 80, 95, 110, 125, 140 K

9. Nonlinear b and a conductivities of TiS3 whiskers at equal E values. Longitudinalσ( measured along b axis). The sample length is 56 µm. Transverse σ ( measured along aaxis). The sample length is 30 µm. Temperature dependences of the linearconductivity σ(0) measured at the current I ≤ 0.1 μA(thick lines) andthe nonlinear part of differential conductivityσn = σd(V) – σd(0) at the specified voltages mentioned atthe corresponding curves(circles) . Thin solid lines are guides foreye. Notice that σb(0) is divided by 100 and σa(0) is divided by 30.

10. Common features: Quasi-one-dimensional structure. 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. Increasein the ab-plane anisotropy of the conductivity with a decreasein the temperature. The anomaly in the ratio ρ/ρ|| at the transition temperature. 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. The temperature dependence of the nonlinear conductivity hasfeatures at the same temperatures as the linear conductivity. Weak temperature and electric field dependences of nonlinear conductivity in high electric fields. Distinguishingfeatures: The resistivity of TiS3 is ρ3002 Ohmxcm, i.e. 3-4 orders of magnitude higher than that of known conductors with the charge density wave. The electron density in TiS3 at roomtemperature determined from the Hall effect isn~21018см-3. To date, the Peierls transition wasobserved only in quasi-one-dimensional conductorswith a relatively high carrier density(n~21021см-3 at T = 300 K). The anisotropy of the conductivity of TiS3 in the ab plane is comparatively smallρa/ρb5at 300 K (3 times smallerthan that of NbSe3and 30 times smaller than that ofTaS3). The zero-voltage peaks instead of the threshold behavior of the current–voltage characteristics. Nonlinear transverse conductivity (along the a-axis) at T<120 K. TiS3 and Paierls conductors.

11. X-ray study of TiS3 whiskers at different temperatures. Scans along a-axis. h00 scan at T=250 K Shubnikov Institute of Crystallography of RAS Low-temperature four-circle diffractometerHuber 5042 Mo-anode h00 scan at T=200 K h00 scan at T=55 K

12. 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) 4.2 K α= 1 140 K T = 4.2, 10, 14, 17, 21, 31, 41, 55, 65, 80, 95, 110, 125, 140 K

13. 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)

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