Jani, A R

Patel, S G

Vaidya, Rajiv

IACS Institutional Repository

UnlumJ P/i.Vi. 79(1), 85-87 (2005) o le^ nTK)N,4^U PGrowth and characterization of NbSe  ^ single crystalsRajiv Vaidya, M ehul^ave. S G Palel=  ^and A R JamDepartment o f  Physics, Saidar Patel lln^ersity, Vallabh Vidyanagar-388 120. Ciujarat, IndiarEmail sh|tnlibhaip&>y ahoo.com  R ercivcu l 26  A p r il 2(104, m  < v p ic d  IS  N o vem h et 2 0 0 4A bstract Single crystals ot niobium diselenide (NbSCj) having a layered structure were grown by chemical vapoui tiansport technique (CVT)using iodine as transporting agent The energy dispersive analysis by X-ray (EDAXj gives the coiifirination alxiut the stoichiomctiy o f the grown single  rystal X ray diffraction (X R D ) studies w eie  performed foi the stiuctural characteri/ation The lattice parameters obtained from the XKD analysis ^^ ere ti ^ 3 4‘) ± 0 058 A and r  O 28 ± 0 058 A. The NbSe, single crystals possess hexagonal crystal structuie The X-iay density was found to he 6 2860  m/em’ and volume was calculated about 66 24 (A)’ The rcsislivily measurements o f the grown crystals weie earned out within the temperature range )t 3(K) K it^  423 K 3>ic crystal.s were found to exhibit semiconducting nature in this range 'I’he behavioui of the resistance undei pressure is ihoioughly  tudicd using Bridgman anvil set iipto 6 5 (JPa 7'he resistance found decreasing as the pressure increases uplo 6 5 fJPa. The crystal shows semiconducting behaviour The implications o f  the results have been discussedK eyw ordsP \ (  S N os.Transition metal d ichalcogenides. X-ray diffraction, Bridgman anvil set up. activation energy 81 05 D /. 81 10 BkThe work has been centered on the layered transition metal dichalcogenides o f  group and VI^. Niobium diselenide (NbSe^) IS a member o f transition metal dichalcogenide (TMDC) group. Transition metal dichalcogenides (TMDC) have various characters of metal, semiconductor, magnetic substances and have been widely studied [ 1“3J. Among the TM DC’s, NbSc2 have layered crystal structure, which are formed of unit layers consisting of transition metal atoms sandwiched by chalcogen atoms [4j. Single crystals of the transition metal dichalcogenides (TMDC) have been prepared by chem ical vapour transport technique using iodine or bromine as transporting agent [5-8J. The epitaxial growth o f  NbSe^ thin film using the vacuum evaporation technique, has been reported (9J. In materials with 'd Strong pressure dependence o f  superconductivity (such as NbSe^), the strain-induced interaction affects the structure of the flux lattice. For the field parallel to the c-axis of NbSe2,lhe Ilux lattice is locked on the crystal. The possible role of an harmonic elastic interactions of vortices is discussed I lOJ. The differential resistance in 2H-NbSe^ single crystals at very low currents, have been probed [ 11J. The layered material NbSCj is a convenient material for studying the quantum oscillations in h^e vortex state [12]. A characteristic structure of the local t '^orresponding Authordensity  o f the sta tes observed  in the layered hexagonal superconductor 2H-NbSc..> by scanning tunneling microscopy (STM) [131. The anisotropic superconductor 2H-NbSe2 (Tc -  7 .IK) has attracted a great deal o f attention over the last few years [ 14-201. The production o f NbSe^- nanotubes by electron ir ra d ia tio n  w as re p o rte d  [211. T he re sp o n se  o f  the  incommensurate charge density wave modulation in the quasi- low dimensional 2H-NbSc2, has been measured using X-rays scattering [221. The results of a study o f vortex arrangements in the peak effect regime of 2H- NbSe^ by Scanning tunneling micro.scopy were presented [23].Single crystals of NbSe^ were grown by a chemical vapour transport technique using iodine as transporting agent. A 5 gm mixture of Nb (Purity: 99.95 %, Make: Reachim, USSR) and Se(Purity: 99.99 %, Make: Aldrich, USA) was filled in the dried ampoule. Iodine of the quantity 5 mg/cc of the ampoule volume was sealed in the thin capillaries and placed in the am poule as transporting agent. Then the ampoule was sealed at the pressure of JO"*' torr. The sealed am{x>ule was introduced into a two-zone furnace at a constant reaction tem perature to obtain the charge of NbSe^. The charge so prepared was rigorously shaken to ensure proper mixing o f the constituents and kept in the furnace again, under appropriate condition to obtain single crystals o f<e>2005IACS8 6 R ajiv Vaidya, M ehul Dave, S  G P atel a n d  A R JaniNbSc2. charge compositions and growth conditions are summarized in Table 1. The chemical composition of the grown samples has been well confirmed by carrying out EDAX analysis as shown in Table 2.T able 1. Growth parameters for NbSc^ sin g le  crystals using chem ical (iodine) vapour transport technique.Am pouledim ensionTemperaturedistributionPhysical characteristics o f  crystalsLength ID mm mmH ot Cold Growth P late T h ick n ess Colourzone zon e tim e area m mK K hr mm22 5 0 22 1 123 1073 2 4 0 0 03 ShiningBlackT kble 2. W eight % o f  e lem en ts taken for grow th and obtained from  EDAX analysisWt(%) o f  elem ents NbSe^Nb SeTakenFrom EDAX37 04  34.3862.9665.62For X-ray diffraction work, several small crystals were finely ground with the help o f an agate mortar and filtered through 106-micron sieve to obtain grains of nearly equal size. X-ray fx>wder patterns were recorded on X-ray Diffractometer (Make: Phillips, Holland and Model: X" Pert) using CuK^radiation.To study the effect o f pressure on resis^nce  o f  these single crystals, we used Bridgman opposed anvil set up. In Bridgman opposed-anvil system [24], the decrease in volume and therefore, the maximum pressure are limited by the flow o f deformable gaskets in various geometries. The sam ple is in the form o f a thin disk surrounded by pyrophyllite gasket [25] with talcum powder as pressure transmitting medium. A four-probe method is used to evaluate the resistance o f the NbSc2 sample up to 6.5 GPa pressure.T he h igh  te m p e ra tu re  fo u r-p ro b e  re s is tiv ity  set up manufactured by Scientific Equipm ents, Roorkee was used to study the variation o f resistivity with tem perature, in the range of 303 K to 423 K.The shining black single crystals o f  N bSc2 were obtained by chemical vapour transport (CVT) technique. The crystalT able 3 . Crystallographic data o f  N b S c2 s in g le  crystals grow n using  chem ical vapour transport technique.Parameter Present worka «b (A) c (A )Unit cell volume (A X-ray density (gip/cm^)3.49 ± 0.058 6.28 ± 0.058 66.24 6.2869Structure o f as grown crystal is hexagonal. The values o f lattice parameters a, b  and c, unit cell volume (V) and X-ray density ( p ) determined from the X-ray diffractograms are presented m Table 3. The X-ray data for NbSe^ was used for the estimation vij particle size using Scherrer’s formula [26],i = • ATAQeosQwhere t is the crystallite size as measured perpendicular to the reflecting plane, K  the Scherrer constant whose value is taken to be unity assum ing the particles to be spherical, A the wave length o f X-ray radiation, P  the half intensity width measured in radians and 0 is the Bragg angle. (// k  /) values corresponding to prominent reflections, ^/-values, peak intensities and particle size for NbSe^ single crystal are shown in Table 4.Tabic 4. X-ray diffraction data for NbSe^ single crystal( h k l ) d-spacing(A )Peak intensity  (counts /sec)Particle size(A)002 6 .4 0 6 9 6 1 7 4  55 2 9 7 .3 40 0 4 3 1728 2 8 8 5  43 303 47101 2 .9 1 5 0 38.34 306  63102 2 7 1 2 7 46 96 307  27103 2 .4 4 2 9 11.74 3 10 .51104 2 .1 7 2 2 32.71 3 1 4 .8 3The graph of resistance v s  pressure for as grown c r y s ta ls  is at room  tem perature show n in F igure 1. The graph shows continuous decrease in resistance with increase in pressuic The graphical variation o f logp  with lOOO/Tis marked in Figure 2 . The activation energy was calculated from the slope o f  this graph and is found to be 0.056 eV.0.8 :0.7 ;0.6 : •3  0.5 :i  0 4  :0.3 :0.2 iO.l :0 -0 1 2  3 4 5 6Pressure (GPa)Figure 1. Plot o f  resistance v.v. pressure for NbScj single crystals at rooii' temperature.We conclude as follows :(i) The chem ical vapour transport technique has been used to grow  the single crystals o f  N bSc2-Growth and characterization of NhSe, single crystals 87(ii)(iii)(iv)optimum condition for the growth of NbSc2 crystal has been found out.The EDAX and XRD study gives confirmation that NbSe^  single crystals are stoichiometrically perfect and the crystal structure of NbSe^  is hexagonal.The resistance decreases as the pressure increases upto 6.5 GPa which shows the semiconducting nafiure of the as grown crystals. The sample becoming more conducting with increase in pressure.The activation energy confirms that NbSe^  beh^es as extrinsic semiconductor in the temperature rj^ ge of 303 K to 423 K.1.6 1 .5 -i 1 41.3-i| l 210.9 ^0.82.50 2.60 2.70 2.80 2.90 3.00 3.10 3.20 3.30 3.4C1000/T(K')figure 2. Vaiiation of resistivity with inverse of temperature in the cinpeiature range of ,”^03 K to 423 K for NbSe2 single crystals\cknowIedgment$The authors are indebted much to DAE-BRNS for providing inancial assistance to Research Project Sanction No. 99/37/28- 3RNS/1004 dated 29-09-1999 for carrying out this work.R eferencesM l F R Gamble et al. S n e m e  174 493 (1971)I 2] B Morosin Aria CryMnllogr B50 551 (1974)( 3J A N  Ve.si rt al. Sow Phws Svmirorui 13 18 (1979)14] J A Wilson and A D Yoffc Adv P hy\ 18 193 (1969)1 51 H Guernoe US G ovt Rvpt 37 101A AD205121 (1961)( 61 R Nitsche et al. J P Im . Cliem Solids 21 199 (1961)(71 H L Urixner J  E lertrorhcin. Sor 110 289 (1963)(81 H vSehafer Chemical Transport Reactions (New York : Academic) (1964)(91 K llneo et al. J. Vac. Sci lech  68 (1990)(10) V G Kogan et al. Phys Rev B51 15344 (1995)(111 G I) Anna et al. Phys Rev B54 6583 (1996)(121 T J B M Janssen et al. Phys Rev B57 11698 (1998)1131 Nobuhiko Hayashi IVIasanon Ichioka and Kazushige Machida Phys. Rev. B56 9052 (1997)(141 P Koorevaar, J Aarts, P Berghuis and f* H Kes Phys Rev. B42 1004 (1990)(15) H Druhs, Z G Xu. J W Brill, L B Delong and J C Hou Phys. Rev B44 4731 (1991)[161 7 G Xu, J - r  Hou. L B Delong and J W Brill Physica C202  256 (1992)(171 S Bhattacharyu and M J Higgins Phys Rev. Lett 70 2617 (1993)(18) S Bhattacharya and M J Higgins Phys Rev B49 10005 (1994)(19) G D’Anna, M O Andre, W Benoit. E Rixlngucz, DS Rtxlriguez, J Luzunaga and J V Wasezak Phy.sica C218 238 (1993)(20) A C  Marley, M J Higgins and S BhatUicharya Phvs Rev. U'tt. 74 320 (1995)(211 M Avalos, Borja E Adem hidlerence Sci Technol (USA) 8 (3143) (2000)(221 C H Da. W J Lin, Y Su and B K Tanncl cf«/. /  P/iv,v Condens M atter (UK)  12 5361 (2000)(23) A M  Troyanovaski, M Van Hecke, N Saha, J Aarts and P H Kes Phys Rev. Lett (USA)  89 147006/1-4 (2002)(24) P W Bridgmann J. Appl. Phys. 12 461 (1941)(25) J Lees Advances in High Pre.ssure Research 1 (1966)(26) S K Snvastava and B N Avasthi J  l^ s s  Com m on Met. 124 85 (1986)

Growth and Characterization of NbSe2 Single Crystals

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/6657/1/Growth%20and%20Characterization%20of%20NbSe2_By%20Rajiv%20Vaidya.pdf

Growth and Characterization of NbSe2 Single Crystals

Abstract

Similar works

Full text

Available Versions

IACS Institutional Repository