Variable Range Hopping Mechanism Research Articles

Electrical conduction in gold nanoparticles embedded indium oxide films: a crossover from metallic to insulating behavior

Electrical conductivity of indium oxide and gold nanoparticles incorporated indium oxide films grown by dc sputtering have been studied in the temperature range 1.5 to 300 K. Films with 0, 6 and 12% gold nanoparticle volume fraction exhibit metallic nature in the temperature interval 1.5 to 20 K, with conduction being governed by electron–electron interaction. Films with 20% gold nanoparticle volume fraction showed insulating nature and the conduction was governed by variable range hopping mechanism in the temperature range 1.5 to 50 K. Furthermore, a crossover from Efros–Shklovskii to Mott type was observed around 15 K. The transition from metallic to insulating nature in spite of the larger gold nanoparticle volume fraction is attributed to the inhibition of oxygen vacancies by Au species during film growth. At higher temperatures, all films exhibit activated conduction.

On the thermoelectric and magnetic properties, hardness, and crystal structure of the higher boride YbB66

In this work we report the results of our investigation of YbB66 as a potential high-temperature thermoelectric material. A high-quality single crystal has been grown by the optical floating zone method. Thermoelectric transport properties were measured in a temperature range of 373–973 K YbB66, like REB66 compounds in general, is a p-type semiconductor whose electrical properties can be described by Mott's variable range hopping mechanism. It shows very large Seebeck coefficient ranging from 588 μV K−1 at 373 K to 241 μV K−1 at 973 K and an electrical resistivity ρ that decreases by almost 4 orders of magnitude from 9.4×10−1 Ω m to 2.4 × 10−4 Ω m. Together with the low thermal conductivity of 2.6 W m−1 K−1 a maximum ZT close to 0.1 around 1000 K was determined with trend of sharp increase toward higher temperatures, which is similar to the previous report of SmB66, and significantly larger than previously reported for Y and Er phases of REB66. However, unlike SmB66, the effective magnetic moment suggests a trivalent state for Yb instead of mixed valence, which was determined by measuring the magnetic susceptibility from 2 to 300 K. The composition of YbB66 was indicated to be metal-rich, which actually may be the origin of the good performance.

Weak antilocalization in Sb2Te3 nano-crystalline topological insulator

Microwave-assisted solvothermal route has been followed to synthesize Sb2Te3 nanomaterial. The morphology and topography of the material have been studied in FESEM and AFM measurements respectively. The optical band gap of the material is found to be ~ 0.25 eV as measured in IR spectroscopy. Temperature dependent resistivity of the nanostructure shows thermal activation behavior in the high temperature region as well as it follows 3D Variable Range Hopping mechanism in the moderate temperature region. Electron-electron interaction and quantum interference dominated upturn in the resistivity is observed at T < 24 K. Low field magnetoconductivity (MC) shows disorder induced weak localization (WL) which makes over to weak antilocalization (WAL) at T ≥ 4 K. MC after post annealing of the sample shows WAL behavior at T < 4 K also. Quantum correction to the low field magnetoconductivity of the material follows Hikami-Larkin-Nagaoka (HLN) equation. The obtained parameters of the HLN equation indicate that the system follows the 2D conduction mechanism and presence of a single conduction channel at low temperature. High field MR exhibits linear and positive magnetoresistance (LPMR) which suggests the survival of robust topological surface state conduction in the nanostructured bulk Sb2Te3 topological insulator.

Leakage mechanism of quasi-vertical GaN Schottky barrier diodes with ultra-low turn-on voltage

The leakage mechanism of quasi-vertical GaN Schottky barrier diodes (SBDs) with ultra-low turn-on voltage has been investigated. By using a tungsten anode, the turn-on voltage is 0.39 V and the average breakdown electric field is above 1 MV cm−1. Under low reverse bias, the thermionic emission is dominated. When the reverse bias increases to a certain value, the increased electric field promotes the electron hopping along the threading dislocation in the bulk GaN layers, and variable range hopping (VRH) becomes the main leakage current mechanism. The leakage difference between tungsten-anode and nickel-anode SBDs is reduced to one order of magnitude due to the VRH mechanism.

Non-equilibrium processing of ferromagnetic heavily reduced graphene oxide

Discovery of ferromagnetism with simultaneous bandgap opening in graphene[1] provides an attractive platform towards multifunctional spintronic devices. However, device integration of graphene and reduced graphene oxide (rGO) is hindered by scalability and high temperature required for reducing GO. In this paper, we present a nonequilibrium approach for direct laser writing heavily reduced GO films by melting amorphous carbon in ambient conditions. Nanosecond laser irradiation melts carbon, which regrows into rGO in low undercooling conditions. These rGO films exhibit room-temperature ferromagnetism with a high saturation magnetization of 7.0 emu/g and 40 Oe coercivity. The intrinsic ferromagnetic ordering triggers a broad negative magnetoresistance (MR) cusp from 20 to 50 K. An anomalous crossover from weak localization (WL) to weak antilocalization (WAL) is observed below 5 K, suggesting a substantial enhancement in spin-orbit coupling strength, opening a new route to access topological states in rGO. The rGO films exhibit 12.6 cm2/Vs electron mobility with n-type carrier concentration of 1.2 × 1021/cc. Raman spectroscopy and temperature-dependent transport investigations in rGO suggest low-disorder, following 2D Mott variable range hopping (VRH) mechanism with a bandgap of ∼0.22 eV and 3 nm localization length. These findings open a definitive pathway for tuning electrical and magnetic properties in graphene-based materials with laser-writing.

Carrier Transport Mechanisms in Ion Implanted and Highly-Doped p-Type 4H-SiC(Al)

Fundamental aspects of transport in Al ion implanted p-type 4H-SiC are briefly reviewed, in the light of recent literature. Particular attention is paid on (i) the Hall factor and (ii) the role of disorder in the onset of a variable range hopping mechanism (VRH) at high temperatures as doping level increases, up to a 2D-VRH induced by extended defects in the heaviest doped samples. The study allowed to understand the critical balance between implanted impurity density and annealing temperature that leads to the searched doping level, ensuring an efficient electrical activation of implanted impurities, on a side, and, on the other side, avoiding stacking faults that cause anisotropic hopping transport.

Investigation of the electrical charge transport mechanism and magnetoresistance response in chloride-doped polyaniline–Fe composite nanofibers

One-dimensional composite nanostructures of chloride-doped polyaniline (PANI-Cl) and Fe nanoparticles (NPs) were fabricated via deposition of Fe NPs onto the PANI nanofiber matrix at room temperature. Morphological and structural characterization performed using microscopic techniques, e.g. scanning electron microscopy and transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy confirmed effective deposition of crystalline Fe NPs onto the amorphous PANI-Cl nanofiber matrix. The temperature-dependent magnetic property measurement results revealed the ferromagnetic nature of the prepared PANI-Cl–Fe composite nanofibers (CNFs) structure. Depending on the Fe NP loading, the PANI-Cl–Fe CNFs showed both metallic and semiconducting behaviour. The temperature-dependent resistivity of semiconducting PANI-Cl–Fe CNFs was best described by Efros–Shklovskii variable range hopping (ES-VRH) and Mott three-dimensional variable range hopping (Mott-3D-VRH) mechanisms at low and high temperature regimes. Magnetoresistance (MR) investigation was executed at different temperatures and magnetic fields for the PANI-Cl–Fe CNF pellets in semiconducting form. Room temperature (300 K) negative MR values were detected in both the low and high magnetic field regions. A significant increase in MR values was noted with a decrease in temperature from 300 K to 5 K. Meanwhile, the observed low-field negative MR behaviour of PANI-Cl–Fe CNFs was explained by the forward interference model. Therefore, the implications of these findings might be significant for the application of PANI-Cl–Fe CNFs as sensing materials for magnetic field sensor devices.

Investigation on the structure and physical properties of Fe3O4/RGO nanocomposites and their photocatalytic application

In the present work, we have investigated the structural, optical, photocatalytic activity, electrical transport and magnetic properties of Fe3O4 nanoparticles and its composite with reduced graphene oxide (Fe3O4/RGO) by varying the ratio of reduced graphene oxide (RGO: 2% and 4%). Fe3O4 nanoparticles and RGO were synthesized by the modified sol-gel and Hummers methods respectively. The as-prepared samples were examined by various analytical techniques to investigate their functional properties and possible applications. Rietveld refinement analysis of the XRD data reveals face-centered cubic (fcc) structure of the Fe3O4 nanoparticles and confirms the characteristic planes of magnetite phase. The average crystallite size of the Fe3O4, Fe3O4/RGO (2%) and Fe3O4/RGO (4%) samples was estimated using Scherrer's equation and found to be ∼10, 15 and 19 nm respectively. TEM/HRTEM micrographs establish spherical shapes of the magnetite nanoparticles with an average diameter of ∼12 nm for Fe3O4, while 17 and 20 nm in the nanocomposites respectively. The low temperature resistivity measurements exhibit semiconducting nature of all the samples and follow variable range hopping (VRH) mechanism. The magnetic measurements demonstrate typical superparamagnetic behavior of the samples at room temperature. The photocatalytic performance of the samples has been investigated for the decolorization of methylene blue (MB) organic dye under visible light irradiation. The Fe3O4/RGO nanocomposites display better adsorption behaviour and excellent photocatalytic activity than RGO and Fe3O4 nanoparticles. This may be due to strong interactions between Fe3O4 nanoparticles and graphene sheets.

Enhanced mobility and controlled transparency in multilayered reduced graphene oxide quantum dots: a charge transport study

Reduced graphene oxide (rGO) layers are known to be significantly conductive along the basal plane throughout delocalized sp2 domains. Defects present in rGO implies in disordered systems with numerous localized sites, resulting in a charge transport governed mainly by a 2D variable range hopping (VRH) mechanism. These characteristics are observed even in multilayered rGO since the through-plane conduction is expected to be insubstantial. Here, we report on the multilayer assembly of functionalized rGO quantum dots (GQDs) presenting 3D VRH transport that endows elevated charge carrier mobility, ca ∼ 236 cm2 V−1 s−1. Polyelectrolyte-wrapped GQDs were assembled by layer-by-layer technique (LbL), ensuring molecular level thickness control for the formed nanostructures, along with the adjustment of the film transparency (up to 92% in the visible region). The small size and the random distribution of GQDs in the LbL structure are believed to overcome the translational disorder in multilayered films, contributing to a 3D interlayer conduction that enhances the electronic properties. Such high-mobility, transparency-tunable films assembled by a cost-effective method possess interesting features and wide applicability in optoelectronics.

Transport Properties of La0.8Sr0.2MnO3 and Bi0.95Dy0.05FeO3 Based (0.5) La0.8Sr0.2MnO3 + (0.5) Bi0.95Dy0.05FeO3 Composite

Here, we report the structural and low temperature electrical properties of La0.8Sr0.2MnO3 (LSMO), Bi0.95Dy0.05FeO3 (BDFO) and their composite (0.5) LSMO + (0.5) BDFO prepared via solid-state reaction route. X-ray diffraction (XRD) data studies infers that both the compounds LSMO and BDFO are single phased in nature. Further XRD data analysis reveal that both these compounds display their presence in the composite sample. Both the parent samples of the composite were observed to have crystallized in rhombohedral (R3c) structure. The lattice structure was further verified via Raman Spectroscopic measurement technique. Low temperature transport properties study establishes the semiconducting nature of the composite. The dc resistivity data of ferromagnetic mettalic LSMO compound suggests that the electron–electron scattering is predominant in the metallic region whereas the semiconducting region in the composite sample [(0.5) LSMO + (0.5) BDFO] is well described using small polaron hopping and Mott’s variable range hopping (VRH) models. Activation energy Ep was found to decrease with increase in magnetic field from 0 to 8T attributed to the decrease in the values of charge localization. The density of states Increases with magnetic field attributed to the suppression of magnetic domain scattering explained via Mott’s VRH mechanism. High MR% is observed in both the LSMO sample and the composite one which increases with decrease in temperature.

Role of phase transition in the dielectric and magnetic properties of Na containing NiO

In this study, we systematically investigated the phase transition (cubic (90°) → rhombohedral (60.01°)) and its role in the electronic structure, dielectric, and magnetic behavior of Ni1−xNaxO (0.02≤x≤0.2). X-ray photoelectron spectroscopy indicated non-local screening of the divalent Ni by oxygen and monovalent sodium ions together with giant multiplet splitting. At 310 K, the longitudinal optical phonon mode (500 cm−1) dominated over all the vibrational excitations, but for the dilute dispersion of Na, the transverse optical phonon mode (455 cm−1) exhibited the highest intensity among all the modes. Even at a very low level (x∼ 0.02) of Na substitution, the intensity of the 2-magnon mode (1530 cm−1) was significantly suppressed. The onset of the structural transition and antiferromagnetic Néel temperature (TN) shifted to a high temperature region with moderate Na substitution, which has significant implications for the dependence of the relative dielectric permittivity (εR(T)) and magnetic susceptibility (χmag(T)) on the temperature. The dependence of the ac-resistivity ρac(T, f) on the temperature and frequency followed Mott's variable range-hopping mechanism for charge carriers between the localized states, where the activation energies were highly dependent on the spin (S = 1/2) of the type-II antiferromagnetic system. The magnetization isotherms (M–H) were analyzed using a modified Langevin function M=MoL(μPHkBT)+χaH and we extracted TN for the Ni1−xNaxO system.

Magnetism and magnetoresistance in Al half doped LaNiO3

Abstract The rhombohedral perovskite LaAl0.5Ni0.5O3 (or La2AlNiO6), synthesized by a combustion method is found to contain Al3+ and Ni3+ cations in the rhombohedral lattice. The material exhibits a temperature dependent (thermally excited) paramagnetic susceptibility and follows the modified Curie-Weiss law implying an antiferromagnetic ordering at very low temperatures. A non-saturating hysteresis loop with a coercivity of 108 Oe is observed at 2 K which is arising from the magnetic contribution from Ni in the lattice. The conduction mechanism in LaAl0.5Ni0.5O3 for 80–300 K follows the Mott's variable range hopping mechanism. A negative magnetoresistance of 1.75% is observed at 2 K under 90 kOe field which decreases linearly by increasing the temperature up to 18 K and then changes to positive with comparatively low value. Both the negative and positive magnetoresistance increases linearly with an applied magnetic field.

Variable-range-hopping conduction and polaron dielectric relaxation in Cu and Nb co-doped BaTiO3

BaTi0.7(Cu0.1Nb0.2)O3 ceramic was prepared using a solid-state method and its structure, valence states, conduction mechanism and dielectric properties were investigated in detail. A fine-grained microstructure and a distorted pseudo-cubic perovskite structure were confirmed by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. X-ray photoelectron spectroscopy analysis suggested that Cu in BaTi0.7(Cu0.1Nb0.2)O3 was polyvalent but the valence states of Ti and Nb were invariable. Mott's variable-range-hopping (VRH) conduction was observed. The two colossal dielectric constant plateaus in low- and high-temperature ranges were ascribed to the electrode and grain boundary responses, respectively. The VRH model described the low-temperature relaxation well, indicating that the dielectric relaxation was a polaron relaxation rather than Maxwell–Wagner type. Both grain and grain boundary resistances were well fitted by the VRH model, suggesting that the VRH mechanism was tenable in both grain and grain boundaries. The electron paramagnetic resonance signal was ascribed to Cu ions, and the linewidth showed a linear relationship with T−1/4, corresponding to the charge transfer between different valence via Cu+-O-Cu2+ and Cu2+-O-Cu3+ paths. The hopping of carriers was also responsible for the conduction and polaron dielectric relaxations.

The influence of the space charge on The Ohm's law conservation in CVD diamond layers

In present work we report the investigation of charge transport mechanism in thin diamonds layer grown by hot filament chemical vapor deposition (HF CVD) method. The measurements were performed in both, wide temperature and bias voltage ranges as well. In the disordered matter the variable range hopping mechanism can play a crucial role. The obtained results reveal that simultaneously holes and electrons are involved in current flow. They can be easily distinguished by their different dynamics detected by impedance spectroscopy. The diamond crystal is considered as a wide bandgap semiconductor. Hole states originated as point defects inside of the bandgap behave like usual charges in semiconductor and they obey the Ohm's law. However, the CVD diamond polycrystalline films always contains some amount of sp2 hybridized amorphous carbon phase. This form of carbon can donate electrons to the system. Electrons gathered as space charge on diamond edges create a depletion layer with unlike properties. The Ohm's law is broken for such type of charges and their activation energy are temperature dependent. At temperature of 21 K a sudden change of surface resistivity is observed, when helium atoms are being adsorbed on slowly moving holes.

Transport Properties in InAs Thin Films with Different Degrees of Disorder Near the Metal–Insulator Transition

Transport properties of Indium Arsenide (InAs) films deposited at different working pressures are investigated in the temperature interval of T ∼ 2–250 K. Electrical transport of InAs films is related to the degree of disorder, which increases as working pressure increases. Activated conductivity models satisfactorily describe conduction in the localized band-tails at high temperatures, while conductivity shows metallic characteristic at low temperatures for μc-InAs samples. The critical conductivity exponent of μc-InAs is close to 1, which indicates that μc-InAs samples exhibit a close proximity to the metal–insulator transition. The product of aB and n1/3 for samples S1 and S2 is 0.236 and 0.207, respectively, which is roughly consistent with the Mott criterion. But for α-InAs samples in the high temperature region, electron transport is described by conduction in extended states and in localized states near the Fermi level. Furthermore, a crossover from Mott variable range hopping (VRH) to the Efros–Shklovskii VRH mechanism is observed in α-InAs thin films at low temperatures.

Studies on transport properties of manganite based nano–micro particles–matrix composites

In this communication, low resistive bulk La0.7Ca0.3MnO3 (LCMO) was prepared by solid state reaction (SSR) route whereas high resistive nanoparticles of LaMnO3 (LMO) was prepared by cost effective sol–gel technique. Composites of LMO and LCMO were prepared by mixing them in different weight ratios, i.e. LMO = 10%, 20% and 30% in LCMO manganite matrix. In the present study, LMO have been used as nanoparticle fillers in the LCMO matrix lattice to study the transport properties of the composites. X–ray diffraction (XRD) measurement reveals the single phasic nature of the composites without any detectable impurity within the measurement range studied. XRD pattern of higher LMO content based composite possesses slightly different structural phases of LMO and LCMO. Resistivity measurement reveals that all the composites exhibit metal to insulator electronic phase transition at respective TP, wherein values of resistivity and TP get modified due to the cooling or heating cycles performed, measurement current used and LMO nanoparticle filler content in the composites. These variations have been discussed in the context of scattering centres created due to the presence of LMO fillers and complex phase separation scenario of the composites. A clear phase separation in higher filler content based composite has been displayed in its resistivity behaviour. To understand the charge transport mechanisms responsible for metallic and insulating (or semiconducting) regions in resistivity behaviours of the composites, most suitable zener double exchange polynomial law and Mott type variable range hopping mechanism were fitted theoretically to the obtained experimental results. Fittings show that spin fluctuations in the composites are highly dependent on the cycles performed, current applied and LMO nanoparticle filler content in the composites. Applied negative and positive current and voltage dependent resistance of the composites reveal the negative electroresistance. Both, resistance of the composites as well as electroresistance are highly affected by the cycles performed, current applied and LMO nanoparticle filler content in the composites understudy. Temperature dependent electroresistance was studied for better insight into an active role of phase separation near electronic phase transition temperatures for all manganite based composites.

Probing of electric and magnetic properties of holmium doped iron oxide nanoparticles

Lanthanide based nanoparticles due to their high magnetic moments and efficient optical properties are potential candidates for various applications. In this paper we report holmium (Ho3+) ion doped iron oxide nanoparticles (NPs) with different concentrations; ⍺-HoxFe2−xO3 (x = 0.00, 0.03, 0.05 and 0.07) synthesized by sol–gel method. The synthesized NPs were studied for dielectric and magnetic properties and were thoroughly characterized using various analytical techniques such as powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), etc. The PXRD confirms hexagonal structure of pure and Ho3+ ion doped iron oxide NPs. The presence of Ho3+ ions was observed by EDS technique. The dielectric studies were carried out at (i) varying temperature (100–400 K) at constant frequency of 100 kHz and (ii) varying frequency (20 Hz–1000 kHz) at constant temperature of 298 K. Both temperature and frequency dependent dielectric studies shows increase in dielectric constant and decrease in dielectric loss with the increase in Ho3+ ion concentration in ⍺-Fe2O3 system. The high values of dielectric constant and low values of dielectric loss at higher frequencies makes these materials as potential candidates for microwave applications. Also the conductivity increases with increase in temperature in the systems studied, indicates semiconducting behavior and decrease in conductivity is observed with Ho3+ ion doping. The conductivity behavior follows Motts law, confirming the variable range hopping mechanism in all the synthesized systems. The magnetic studies shows that the addition of Ho3+ ions in ⍺-Fe2O3 lattice significantly modifies the magnetic properties. On comparing to pure phase, an increase in saturation magnetization was observed for all the samples with Ho3+ ion doping.

Ferroelectric and magneto-dielectric properties of yttrium doped BaTiO3–CoFe2O4 multiferroic composite

Multiferroic composites of ferroelectric and ferrite phases having general formula xCoY0.1Fe1.9O4—(1 − x) Ba0.95Y0.05TiO3 (where x = 0.05, 0.1 and 0.15) were prepared using the conventional solid-state reaction method. X-ray diffraction studies were done to confirm the presence of constituent phases. The microstructural analysis revealed an increase in density with the increase of ferrite content in the ferroelectric matrix. Dielectric studies of the composites, in the temperature range 100–550 K revealed two ferroelectric phase transitions. Variation of dielectric constant and dielectric loss with frequency in the range of 20–3 MHz was carried out at room temperature. The low-temperature dc conductivity behaviour follows Motts law, confirming the variable range hopping mechanism in all the composites. All the composites showed P–E and M–H hysteresis loops; which confirm the ferroelectric and ferrimagnetic nature of the composites. At temperatures below 173 K, an increase in coercivity and saturation magnetization is observed due to frozen spins. The coupling between ferroelectric and ferromagnetic ordering was confirmed by room temperature magneto-dielectric studies. The decrease in real part of dielectric constant and dielectric loss was observed with an increase in the applied magnetic field. An appreciable increase in percentage magneto-capacitance was observed at lower frequencies and with the increase of ferrite content in the composites. The magneto-electric coupling coefficient was calculated by using the expansion of the thermodynamic potential φ (for x = 0.15) and was found to be 3.397 × 10−2 (emu/g)−2.

Effect of structural disorder on transport properties of LaNiO3 thin films

We have deposited LaNiO3 thin films on LaAlO3 (001), SrTiO3 (001), and Si (001) substrates using the pulsed laser deposition technique. Depositions were carried out at various substrate temperatures ranging from 0 to 800 °C. The effects of lattice mismatch and structural disorder on the transport properties of films deposited on various substrates and at different substrate temperatures are reported. X-ray diffraction confirms a highly c-axis oriented growth of LaNiO3 films on all the substrates at substrate temperatures of 600 and 800 °C, while at lower substrate temperatures deposited films are amorphous. Emergence of a new Raman mode indicates symmetry lowering in all the deposited crystalline films. Hardening of the Eg(3) (∼400 cm−1) mode is also observed with the rise of in-plane compressive strain. Resistivity curves for films on Si show a semiconducting behaviour and follow a variable range hopping mechanism. Crystalline films on LaAlO3 and SrTiO3 exhibit a metallic character along with a low-temperature resistivity upturn, which is attributed to the contribution of self-localization to resistivity at low temperatures as indicated by magnetotransport measurements.

Influence of sulfur doping on the electrical and thermal transport properties of FeTe1-xSx superconductors

In this study, we determined the structural, electrical, and thermal transport properties of the FeTe1−xSx system, where x = 0.0, 0.1, 0.2, and 0.3. The samples were synthesized using a standard solid-state reaction route via vacuum encapsulation and characterized by X-ray diffraction, which indicated a tetragonal phase with the P4/nmm space group. The parent compound FeTe exhibited an anomaly according to the resistivity measurements at around 67 K due to structural change. The S-substituted samples exhibited negative dependence on the temperature at an electrical resistivity above 10 K, and quantitative analysis indicated that the variable range hopping mechanism governs electrical conduction in the FeTe1−xSx system. In the low-temperature regime, the Seebeck coefficient, S(T), had an anomalous dip feature with crossover of the sign, which can be understood based on the phonon drag contributions and the multiband picture, respectively. The lattice phonons made major contributions to the measured thermal conductivity, κ(T). In addition, we observed a reduction in the height of the low-temperature phonon peak with κ due to the substitution of S for Te, thereby indicating strong enhancement of the disorder-induced phonon scattering. Moreover, a positive dκ/dT was observed in the normal state, which might be related to local anharmonic lattice distortions. Overall, based on our analyses, we conclude that phonons play important roles in the transport properties of FeTe1-xSx superconductors.