• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Electron delocalization enhances the thermoelectric performance of misfit layer compound(Sn1-xBixS)1.2(TiS2)2

    2022-11-21 09:40:26XinZhao趙昕XuanweiZhao趙軒為LiweiLin林黎蔚DingRen任丁BoLiu劉波andRanAng昂然
    Chinese Physics B 2022年11期
    關(guān)鍵詞:劉波

    Xin Zhao(趙昕) Xuanwei Zhao(趙軒為) Liwei Lin(林黎蔚) Ding Ren(任丁)Bo Liu(劉波) and Ran Ang(昂然)

    1Key Laboratory of Radiation Physics and Technology,Ministry of Education,Institute of Nuclear Science and Technology,Sichuan University,Chengdu 610064,China

    2Institute of New Energy and Low-Carbon Technology,Sichuan University,Chengdu 610065,China

    The misfit layer compound(SnS)1.2(TiS2)2 is a promising low-cost thermoelectric material because of its low thermal conductivity derived from the superlattice-like structure. However,the strong covalent bonds within each constituent layer highly localize the electrons thereby it is highly challenging to optimize the power factor by doping or alloying. Here,we show that Bi doping at the Sn site markedly breaks the covalent bonds networks and highly delocalizes the electrons. This results in a high charge carrier concentration and enhanced power factor throughout the whole temperature range.It is highly remarkable that Bi doping also significantly reduces the thermal conductivity by suppressing the heat conduction carried by phonons,indicating that it independently modulates phonon and charge transport properties. These effects collectively give rise to a maximum ZT of 0.3 at 720 K.In addition, we apply the single Kane band model and the Debye–Callaway model to clarify the electron and phonon transport mechanisms in the misfit layer compound(SnS)1.2(TiS2)2.

    Keywords: misfit layer sulfide,electron delocalization,carrier mobility,chemical bond

    1. Introduction

    Over 60%fossil fuels input for power generation is being rejected as low-grade heat annually.[1]Thermoelectric materials are able to directly convert such a huge amount of heat into utilizable electricity[2]without releasing any chemical residuals, showing great potential to contribute to solving the energy problem at present.[3,4]The efficiency of a thermoelectric device primary depends on the figure of merit, namely,ZT, of the thermoelectric materials used, which is defined asZT=S2σT/κtot,[4]whereSrepresents Seebeck coefficient,σdenotes electrical conductivity, their productS2σis called power factor,Tis the absolute temperature,andκtotis the total thermal conductivity with contribution from both charge carriers(κele)and phonons(κlat).

    In the past decades, theZTvalues of representative thermoelectric compounds have been considerably improved by applying innovative strategies, such as optimizing electrical transport properties[5–10]or suppressingκlat.[11,12]However, the majority thermoelectric materials contain toxic or expensive elements. For extensive application, thermoelectric community currently puts interest on searching economically-viable, environmentally benign thermoelectric materials.[13–15]The surprising and promising examples are the discovery of Mg3Sb2[8,16–18]and SnSe[19–22]based compounds with intrinsically low thermal conductivity. The former shows exceptionally highZTvalue of~1.5 around room temperature,exceeded conventional expensive Bi2Te3.[8,16,17]The latter exhibits extraordinary performance over a broad temperature window. Besides, the study of the physical mechanisms of novel materials is also very important. The single crystal 1T-TaS2sample exhibits strong coupling between phonon excitation and commensurate charge-densitywave lattice,which provides a deep insight into close association between electronic correlation and dynamical motions of phonons.[23]These findings unambiguously highlight the importance of discovering new compounds.

    (SnS)1.2(TiS2)2is an n-type misfit layer semiconductor built by alternately stacking two atomically thin TiS2slabs with a van der Waals (vdW) gap and SnS monolayer along theccrystallographic direction. Given the abundant interface formed between the TiS2and SnS layer,it shows intrinsically low thermal conductivity compared with other thermoelectric sulfides.[24,25]However, it is highly challenging to optimize its power factor because the metal cation easily forms covalent bonds with sulfur, highly localizing the electrons. For example, (Sn0.96Sb0.04S)1.2(TiS2)2shows carrier concentration nearly the same to the pristine one.[26]Here, we reveal that Bi doping can effectively improve the carrier concentration without degrading the carrier mobility by delocalizing the surrounding electrons. This gives rise to an enhanced power factor over the entire temperature investigated. Remarkably,the heavy Bi atom also significantly decreases the lattice thermal conductivity by generating point defects.[27]As a result,(Sn0.96Bi0.04S)1.2(TiS2)2shows aZTvalue of 0.3 at 723 K,one of the highest values reported in this compound.

    2. Experimental details

    2.1. Synthesis and sample preparation

    The appropriate molar ratio of high purity elements of tin (99.99%, aladdin), titanium (99.99%, aladdin), sulfur (99.99%, aladdin) and bismuth (99.999%, aladdin) corresponding to (Sn1-xBixS)1.2(TiS2)2(x= 0,0.02,0.04,0.06)was sealed in a quartz tube under a high vacuum(~10-4Pa).To minimize the risk of explosion, the sealed tubes were slowly heated to 773 K and dwelled for 12 h, afterward the temperature was raised to 1073 K and allowed to react for 48 h,and naturally cooled down to ambient temperature. The obtained ingots were hand-ground into fine powders in air using an agate and pestle. The resulting fine powder was loaded into a graphite die mold and hot pressed at 923 K for 45 min under an axial pressure of 50 MPa in a dynamic vacuum. The density of the sample was determined by the geometrical dimensions and masses, showing all the samples have density higher than 97.3%of the theoretical value.

    2.2. Powder x-ray diffraction

    The pulverized samples were used for powder x-ray diffraction (XRD). The powder diffraction patterns were recorded with CuKα(λ=1.5418 ?A) radiation in a reflection geometry on an Inel diffractometer operating at 40 kV and 20 mA (DX-2700 x-ray diffractometer). All measured samples are single phase within the detection limit of our laboratory XRD instrument,showing none of detectable secondary phases and unreacted elements.

    2.3. Charge carrier transport

    The densified samples were cut into different shapes using a wire saw for charge and thermal transport properties measurement respectively. The rectangular bar with the dimension of 2×3×8 mm3was used for simultaneously measuring the electrical conductivity and Seebeck coefficient employing a CTApro instrument under a low-pressure helium atmosphere from 320 K to 720 K.The Hall charge carrier concentration and mobility were measured from 320 K to 720 K by a home-built apparatus with a unidirectional 1.5 T magnetic field under a high vacuum.

    2.4. Thermal conductivity

    Thermal diffusivities with respect to temperature were measured using disks with a diameter of 6 mm or 8 mm and a thickness of 1.5 mm using the laser flash diffusivity method on a Netzsch LFA 467 instrument. The surface of the disks was protected by a thin layer of graphite to minimize the thermal radiation at elevate temperature. The thermal conductivity was calculated by the equationκtot=ρ·D·Cp,whereρis the mass density,Dis the measured thermal diffusivity, andCprepresents the temperature-dependent heat capacity that can be determined byCp= [0.17078+(2.64876×10-5)×T]J·g-1·K-1,whereTis the absolute temperature. The electrical contribution to the total thermal conductivity was calculated based on the relationκele=LσT,whereLis the Lorenz number estimated using a single parabolic band(see supporting information for the details),σis the electrical conductivity,andTis the absolute temperature. Lattice thermal conductivityκlatwas calculated by the relationκlat=κtot-κele.

    2.5. Electronic structure calculation

    The first-principles calculations were performed by utilizing the Perdew–Burke–Ernzerhof (PBE)[28]formalism and generalized gradient approximation (GGA)[29,30]implemented in Viennaab initiosimulation package (VASP)[31,32]code. The plane-wave basis was truncated at the energy cutoff of 600 eV. To reduce the computational load, we only sampled the momentum space at theΓ-point and a 4×1×1 mesh.All geometry structures were fully relaxed until the calculated Hellmann–Feynman force on every atom were less than 0.03 eV·?A-1under the convergence condition of 10-4eV.

    3. Results and discussion

    Covalent bonds in(SnS)1.2(TiS2)2strongly trap the electrons so that softening these bonds may release the localized electrons. Note that, the bond dissociation energy for Bi–S is 315 kJ·mol-1, much lower than 467 kJ·mol-1for Sn–S and 387 kJ·mol-1for Sb–S.[33]This indicates Bi doping can weaken the covalent bonds and give rise to a higher carrier concentration than the Sb doped system. To verify our hypothesis,we synthesized samples with the composition of (Sn1-xBixS)1.2(TiS2)2(x=0,0.02,0.04,0.06) using hightemperature solid-state reaction.All the phases can be fully indexed as the misfit layer structure,showing neither detectable impurity phases nor unreacted residual within the resolution limit of lab XRD measurements (Fig. 1(a) and Fig. S1). To accurately determine the lattice parameter, we performed Rietveld refinement on the recorded XRD patterns(Fig.S2 and Table S1). The refined unit cell dimensions gradually shrink as the Bi content increases, suggesting that Bi atoms are homogenously dissolved over the matrix apparently (Fig. 1(b)).This finding agrees well with the microscopic elemental map collected by scanning electron microscopy equipped with an energy dispersive spectroscopy(SEM-EDS,Fig.S3).

    Fig. 1. (a) Powder XRD patterns of (Sn1-xBixS)1.2(TiS2) samples (x =0,0.02,0.04,0.06). (b)Lattice parameters with respect to the Bi content.

    Trivalent Bi3+substituting divalent Sn2+could increase charge carrier properties significantly. In accordance,we measured the temperature-dependent Hall carrier concentration and mobility for the (Sn1-xBixS)1.2(TiS2)2(x=0,0.02,0.04,0.06) samples. Note that although we measured all properties along both parallel and perpendicular to the hot press direction, we will mainly concentrate on those perpendicular to the press direction because it shows higherZT. The transport properties collected parallel to the press direction are shown in Fig.S4.As the concentration of Bi doping increases,we can see an enhancement of the electrical properties. This is consistent with the results observed in the in-plane, which also can confirm our hypothesis.

    All samples show nearly constant Hall carrier concentration (nH) over the entire temperature range investigated, and their values monotonously increase with higher Bi concentration (Fig. 2(a)). It should be noted that the electron doping efficiency,namely,the number of electrons per Bi atom to the matrix is markedly higher than previously reported values for other dopants in(SnS)1.2(TiS2)-based materials. For example,x=0.04 sample showsnHof 1.8×1021cm-3at 300 K, indicating its electron doping efficiency amounts to 0.63 e-. In sharp contrast,(Sn0.96Sb0.04S)1.2(TiS2)exhibits annHclose to the matrix at 300 K as indicated by the green dashed line,[26]revealing Sb has negligible electron doping efficiency. These verify that Bi atom acts as an efficient electron donor to the(SnS)1.2(TiS2)lattice.

    Fig.2. Charge transport properties of the(Sn1-xBixS)1.2(TiS2)2 samples(x=0,0.02,0.04,0.06). (a)Temperature-dependent Hall carrier concentration nH. The experimental data of(Sn0.96Sb0.04S)1.2(TiS2)2 from previously report is included for comparison(green dashed line).[26] (b)Temperature dependent Hall mobility μH, (c) conductivity σ and (d) Seebeck coefficient. (e) Carrier concentration-dependent Seebeck coefficient at 320 K and 720 K.(f)Temperature-dependent power factor.

    Although Bi doping considerably increases thenH, it marginally reduces the charge carrier mobility (μH). In fact,all samples exhibit nearly identicalμHover the entire temperature range (Fig. 2(b)). Their values rapidly drop with the raising temperature, following the same power law trend of~T-1.5over the entire temperature range, which evident the phonon scattering dominates the charge carrier scattering.This observation confirms Bi uniformly spreading over the crystalline matrix,rather than forming secondary phases or aggregate at the grain boundary,otherwise theμHwould be significantly decreased. Indeed,it contrasts with the general understanding that increasing charge carrier concentration usually decreases with raisingnHbecause of enhanced carrier–carrier scattering, implying Bi doping marginally affects the charge carrier transport.

    Figure 2(c) shows the electrical conductivity (σ) with respect to temperature for the (Sn1-xBixS)1.2(TiS2)2(x=0,0.02,0.04,0.06)samples. Because Bi doping markedly improves thenHwith negligible degradingμHin the full temperature range,it gives rise to higherσat every single temperature point compared to the pristine sample. For example,theσof the title compound(Sn0.96Bi0.04S)1.2(TiS2)is~1100 S·cm-1and~300 S·cm-1at 300 K and 723 K, respectively, much higher than~900 S·cm-1and 250 S·cm-1at the same temperature for the pristine sample.

    The Seebeck coefficient(S)of all samples is negative over the entire temperature range, demonstrating they are n-type semiconductor(Fig.2(d)).Note that Bi doping marginally impacts the magnitude of Seebeck among samples because all the samples have very highnHon the order of~1021cm-3. To examine any possible modulation in electron effective massm*, we calculated the theoretical Pisarenko relation betweenSandnHfor undoped (SnS)1.2(TiS2) in the frame of single Kane band model by assuming that the phonon scattering governs the charge carrier scattering. The black and red lines denotem*=4meat 320 K andm*=5meat 720 K,respectively(Fig.2(e)).TheSvalues for all the samples in this work match well on the lines, suggesting that doped Bi does not alter the band structure in the vicinity of the Fermi level.

    Due to the doped Bi considerably increasesσwithout significantly reducingS,it optimizes the power factor particularly for the best composition(Sn0.96Bi0.04S)1.2(TiS2)(Fig.2(f)).In fact,the(Sn0.96Bi0.04S)1.2(TiS2)sample shows a power factor higher than the pristine one over the entire temperature range.Note that it is challenging to improve the power factor of misfit layer compounds because the highly distorted interface derived from the constituent layers typically leads to a very low electrical conductivity and thereby a low power factor.

    To better understand the enhanced charge transport properties in the (Sn1-xBixS)1.2(TiS2)2compounds, we carried out first-principles calculation within density functional theory regime. Given the high electron doping efficiency as we discussed earlier,the doped Bi atom was placed at the Sn site to mimic the experimental observation. We first analyzed the charge transfer in Bi doped (SnS)1.2(TiS2) for examining the possible charge transfer between Bi and the matrix. For clarity,we only display the charge transfer between one TiS2layer and its neighboring SnS slab(Fig.3(a)). The result shows that the electrons of Bi flow toward the nearest sulfur atom in the adjunct TiS2layer as indicated by the blue ellipsoid, forming electronic bridge to connect large van der Waals gap and facilitate the charge transfer over the matrix. For comparison,we also similarly calculated the Sb doped (SnS)1.2(TiS2). It reveals that the electrons from Sb atom are isolated between the van der Waals gap.

    Fig.3. The charge transfer analysis for(a)Bi and(b)Sb doped(SnS)1.2(TiS2). The Sn,Ti,S,Bi and Sb atoms are depicted by grey,blue,yellow,violet, and orange spheres, respectively. Blue ellipsoids surrounding the atoms denote a loss of electrons. Electron localization function (ELF)contour mapped along the〈100〉z(mì)one axis for(a)Bi and(b)Sb doped(SnS)1.2(TiS2). ELF values ranging from 0 to 1 are depicted by the color bar shown in(c), where blue color denotes the electrons with almost no localization or no electrons, and the red color corresponds to the perfect localization of electrons. The red arrow in (c) indicates Bi substituting Sn delocalized electrons. The black arrow in (d) points out the Sb atom forms covalent bond with adjunct sulfur atom,which heavily localized the electrons.

    It is worth noting that quantitative Bader charge transfer analysis shows that Bi donates 1.27 e-to the interacting S atom,coincidentally to the value of 1.28 e-of Sb transferred to the system. This supports our hypothesis that Bi doping weakly localized the electrons. We calculated the electron localization function(ELF)for both Bi and Sb doped systems(Figs.3(c)and 3(d)). This measures the electron localization in atomic and molecular systems, directly evaluating the chemical interaction between the adjunct atoms.[34]The magnitude of ELF increases from 0 to 1 which denotes the electron transiting from no localization to perfect localization and is visualized by the color code varying from blue to red color. The ELF contour mapped along the〈100〉z(mì)one axis of Bi doped system reveals the ELF value between Bi and S atoms smaller than 0.5 (Fig. 3(c)). This indicates that electrons surrounding Bi are highly mobile,consistent with our observation that incorporating Bi atom negligibly affectsμH.By contrast,electron localization domains are clearly observed between Sb and S atoms in Sb doped(SnS)1.2(TiS2)as indicated by the black arrow. This suggests that the Sb atom is prone to form covalent bond with nearby sulfur atom,trapping the free electrons and reducing the electron doping efficiency. In fact, the EFL results agree well with the fact that the Bi–S bond has lower enthalpy and dissociation energy than the Sb–S bond as we discussed in the previously section, confirming that the weak bond contributes to the exceptionally charge transfer of Bi.

    Figure 4(a)presents temperature-dependent total thermal conductivity(κtot)for the(Sn1-xBixS)1.2(TiS2)2samples(x=0,0.02,0.04,0.06). It is highly remarkable that all Bi-doped samples show suppressedκtotcompared with the pristine sample despite they exhibit much higherσthan the latter.This observation implies that the Bi doping significantly impedes heat conduction by phonons. As a result, we extracted the lattice thermal conductivityκlatby invoking the Widemann–Franz law to subtract electronic thermal conductivityκelefromκtot(see Appendix A for details). All doped samples show much lowerκlatthan the undoped one(Fig.4(b)). For example,theκlatat 320 K markedly decreases from~1.7 W·m-1·K-1for thex=0 sample to~1.2 W·m-1·K-1for thex=0.04 sample. To better understand the effect of Bi doping on thermal conductivity,we calculated the temperature-dependentκlatby the Debye–Callaway model. The black line represents the calculatedκlatfor the pristine sample (Fig. 4(b)), which only considers Umklapp (U) and normal (N) processes. The calculated results fit well with the experimental value, reflecting that the U and N processes dominate the phonon scattering. Since neither secondary phase nor element aggregation is present in the Bi doped samples, we further introduced point defects to the Bi doped system as indicated by the red dash line. The calculated value for thex= 0.04 sample lies far below the pristine one, supporting that the point defect contributes significantly to reducingκlat. In fact, the title compound (Sn0.96Bi0.04S)1.2(TiS2)2shows much lowerκlatthan that of previously reported thermoelectric sulfides(Fig.4(c)).Similarly,the out-of-planeκtotis reached 0.7 W·m-1·K-1for thex=0.04 sample at 723 K,as shown in Fig.S4(e).It should be noted that these data are close to our previous work about(Sn1-xSbxS)1.2(TiS2)2and reflect the good reproducibility of the series of works.[26]

    Fig. 4. Temperature-dependent (a) total thermal conductivity κtot and (b) lattice thermal conductivity κlat for (Sn1-xBixS)1.2(TiS2)2 (x =0,0.02,0.04,0.06). The black and red dashed lines correspond to the calculated temperature-dependent κlat for the pristine and x=0.04 samples using the Debye–Callaway model. (c)A κlat comparison with typical thermoelectric sulfides including TiS2[25] and PbS.[24]

    Fig. 5. Temperature-dependent ZT of (Sn1-xBixS)1.2(TiS2)2 (x =0,0.02,0.04,0.06)samples. The ZT values of pristine TiS2[25] and SnS[35]are given for comparison.

    Figure 5 shows the temperature-dependent dimensionless figure of merit,ZT, for the (Sn1-xBixS)1.2(TiS2)2samples (x= 0,0.02,0.04,0.06). The (Sn0.96Bi0.04S)1.2(TiS2)2exhibits higherZTvalues over the entire temperature range with a maximum reaching to 0.3 at 720 K. It is one of the highest among misfit layer compounds. The achieved performance out-performs previously reported TiS2and state-of-theart polycrystalline SnS,indicating its great potential as a lowcost thermoelectric material for power generation.

    4. Conclusions

    Misfit layer compounds emerge as promising low-cost thermoelectric sulfides. However, it is challenging to optimize its carrier concentration because dopants tend to form covalent bond with sulfur. We demonstrated that Bi weakly bonded with sulfur, delocalized the charge carrier and facilitated the charge transfer. Highly mobile electrons significantly enhanced electrical conductivity and power factor of(Sn0.96Bi0.04S)1.2(TiS2)2over the entire temperature range.The heavy Bi atom also exceptionally reducedκlatby introducing mass fluctuation. By virtue of the Bi doping on charge and thermal transport properties,(Sn0.96Bi0.04S)1.2(TiS2)2shows a maximumZTof 0.3 at 720 K,excelling many state-of-the-art thermoelectric sulfides including SnS and PbS.

    Appendix A

    Density of state mass calculation

    The density of state mass(m*)is calculated according to the following equations[36,37]using the Seebeck coefficient(S)and carrier concentration(nH):

    whereμis the reduced Fermi level,Fj(μ) is the Fermi integral,kBis the Boltzmann constant,his the Planck constant,andλ=0 is the scattering parameter corresponding to acoustic phonon scattering.

    Lorenz number calculation

    The Lorenz numberLwas obtained by single parabolic band(SPB)model with acoustic scattering(λ=0 for acoustic phonon scattering):

    The disorder scattering parameterΓcalcis calculated by the model of Slack[43]and by Abeles[42]assumingΓcalc=ΓM+ΓS,whereΓMandΓSare mass fluctuations scattering parameter and strain field fluctuations scattering parameter, respectively. The mass and strain fluctuation scattering parameters are determined by[40]

    Acknowledgments

    This work was financially supported by the National Key Research and Development Program of China (Grant No. 2018YFA0702100), the Joint Funds of the National Natural Science Foundation of China and the Chinese Academy of Sciences’ Large-Scale Scientific Facility (Grant No. U1932106), and the Sichuan University Innovation Research Program of China(Grant No.2020SCUNL112).

    猜你喜歡
    劉波
    汪安陽 劉波設(shè)計(jì)作品
    毛紡科技(2023年1期)2023-02-24 00:37:40
    劉波作品
    國(guó)畫家(2023年1期)2023-02-16 07:57:50
    Performance and stability-enhanced inorganic perovskite light-emitting devices by employing triton X-100?
    Retrieval of multiple scattering contrast from x-ray analyzer-based imaging*
    晚霞
    赤水源(2018年6期)2018-12-06 08:38:08
    劉波:大海與我作伴
    商周刊(2017年16期)2017-10-10 01:32:47
    千萬別動(dòng)手
    “故事大王”講故事
    大連大學(xué)美術(shù)學(xué)院劉波繪畫作品選
    女人的復(fù)仇
    国产激情久久老熟女| av片东京热男人的天堂| 岛国在线免费视频观看| 精品久久久久久久毛片微露脸| 五月伊人婷婷丁香| 男人舔女人下体高潮全视频| 一a级毛片在线观看| 少妇粗大呻吟视频| 久久久久久九九精品二区国产 | 国产亚洲精品第一综合不卡| 麻豆成人av在线观看| 又黄又爽又免费观看的视频| 亚洲一区二区三区不卡视频| 免费在线观看视频国产中文字幕亚洲| 亚洲熟女毛片儿| 国产精品综合久久久久久久免费| 精品第一国产精品| 亚洲男人的天堂狠狠| 嫁个100分男人电影在线观看| 日韩欧美一区二区三区在线观看| 欧美性长视频在线观看| 精品日产1卡2卡| 99riav亚洲国产免费| 亚洲国产欧美人成| 搡老岳熟女国产| 国产精品久久久久久亚洲av鲁大| 女同久久另类99精品国产91| 亚洲色图av天堂| 欧美日韩瑟瑟在线播放| 99国产精品一区二区三区| 欧美乱色亚洲激情| 香蕉国产在线看| 一边摸一边抽搐一进一小说| 一个人免费在线观看的高清视频| 亚洲激情在线av| 丝袜美腿诱惑在线| 国模一区二区三区四区视频 | 亚洲精品中文字幕一二三四区| 男女视频在线观看网站免费 | 动漫黄色视频在线观看| 午夜福利在线在线| 亚洲男人天堂网一区| 国产一区在线观看成人免费| 五月玫瑰六月丁香| 亚洲男人天堂网一区| 俄罗斯特黄特色一大片| 69av精品久久久久久| 日韩三级视频一区二区三区| 亚洲国产欧美人成| 一夜夜www| 母亲3免费完整高清在线观看| 麻豆国产97在线/欧美 | 日韩有码中文字幕| 国产片内射在线| 可以在线观看毛片的网站| 亚洲最大成人中文| 亚洲精品一区av在线观看| 18禁观看日本| 少妇人妻一区二区三区视频| 午夜影院日韩av| 久久精品国产亚洲av香蕉五月| 国产av不卡久久| 黄频高清免费视频| 亚洲精品中文字幕一二三四区| 最近最新中文字幕大全免费视频| 免费高清视频大片| 国产精品日韩av在线免费观看| 他把我摸到了高潮在线观看| 久久久国产欧美日韩av| 成人国产一区最新在线观看| 此物有八面人人有两片| 亚洲专区中文字幕在线| 亚洲专区中文字幕在线| 婷婷精品国产亚洲av在线| 国产亚洲精品第一综合不卡| 97人妻精品一区二区三区麻豆| 日本 av在线| 淫秽高清视频在线观看| 一进一出抽搐动态| 黑人操中国人逼视频| 大型黄色视频在线免费观看| 国产高清视频在线观看网站| 男人的好看免费观看在线视频 | 久久亚洲精品不卡| 免费人成视频x8x8入口观看| 色av中文字幕| 又紧又爽又黄一区二区| 免费av毛片视频| www.www免费av| 最近最新中文字幕大全电影3| 精品不卡国产一区二区三区| 免费av毛片视频| 久久九九热精品免费| 久久午夜综合久久蜜桃| 熟女电影av网| 亚洲熟妇中文字幕五十中出| 两性夫妻黄色片| 亚洲 欧美一区二区三区| 欧美丝袜亚洲另类 | 成年版毛片免费区| 国产欧美日韩一区二区三| 一个人观看的视频www高清免费观看 | 天堂√8在线中文| 欧美日韩一级在线毛片| 真人做人爱边吃奶动态| 亚洲精品在线观看二区| 久久中文字幕一级| 熟女少妇亚洲综合色aaa.| 女人爽到高潮嗷嗷叫在线视频| 人人妻,人人澡人人爽秒播| 亚洲av日韩精品久久久久久密| 在线观看免费午夜福利视频| 一区二区三区国产精品乱码| 国产av在哪里看| 免费看美女性在线毛片视频| 久久久久性生活片| www日本在线高清视频| 99re在线观看精品视频| 啪啪无遮挡十八禁网站| 中文字幕最新亚洲高清| 一边摸一边做爽爽视频免费| 国产精品一及| 精品熟女少妇八av免费久了| 一级毛片高清免费大全| 国产爱豆传媒在线观看 | 亚洲av成人精品一区久久| 男插女下体视频免费在线播放| av国产免费在线观看| 日本黄色视频三级网站网址| 欧美乱色亚洲激情| 亚洲国产欧美网| 97碰自拍视频| 丰满人妻一区二区三区视频av | 亚洲一区高清亚洲精品| 特大巨黑吊av在线直播| 亚洲 欧美一区二区三区| 熟妇人妻久久中文字幕3abv| 悠悠久久av| 丰满人妻一区二区三区视频av | 日韩欧美国产在线观看| 一区二区三区国产精品乱码| 老司机在亚洲福利影院| 久久精品91蜜桃| 国产av一区二区精品久久| 国产精品爽爽va在线观看网站| 欧美成狂野欧美在线观看| 97超级碰碰碰精品色视频在线观看| 精品国产乱子伦一区二区三区| 黄色成人免费大全| 久久精品夜夜夜夜夜久久蜜豆 | 成人国语在线视频| 久久热在线av| 黄色成人免费大全| 草草在线视频免费看| 久久精品aⅴ一区二区三区四区| av国产免费在线观看| 亚洲乱码一区二区免费版| 国产在线观看jvid| 变态另类丝袜制服| 亚洲五月婷婷丁香| 中文在线观看免费www的网站 | 国产亚洲精品久久久久5区| 亚洲五月天丁香| 免费看日本二区| 伦理电影免费视频| 国产精品一区二区免费欧美| 制服人妻中文乱码| 一本综合久久免费| 国产精品 欧美亚洲| 免费在线观看日本一区| 中文字幕高清在线视频| 日本在线视频免费播放| 欧美色欧美亚洲另类二区| 国产69精品久久久久777片 | 舔av片在线| 免费观看人在逋| 国产成人影院久久av| 精品欧美国产一区二区三| 久久久国产成人精品二区| 黑人欧美特级aaaaaa片| 欧美性长视频在线观看| 色哟哟哟哟哟哟| 一进一出好大好爽视频| 久久久精品欧美日韩精品| 啪啪无遮挡十八禁网站| 99久久国产精品久久久| 成人18禁高潮啪啪吃奶动态图| 免费无遮挡裸体视频| 久久精品人妻少妇| 精品乱码久久久久久99久播| 国产成人精品无人区| 免费看十八禁软件| 亚洲一区高清亚洲精品| 日本在线视频免费播放| 中文字幕av在线有码专区| 男女那种视频在线观看| 黄色a级毛片大全视频| 91大片在线观看| 午夜日韩欧美国产| 免费在线观看影片大全网站| 久久久久久人人人人人| 午夜视频精品福利| www.自偷自拍.com| 好男人在线观看高清免费视频| 长腿黑丝高跟| 欧美一区二区国产精品久久精品 | 两性夫妻黄色片| 最近最新中文字幕大全电影3| 久久精品国产综合久久久| 妹子高潮喷水视频| 国产av一区二区精品久久| 一个人免费在线观看电影 | 成年女人毛片免费观看观看9| 国产99久久九九免费精品| 国产精品99久久99久久久不卡| 亚洲av成人不卡在线观看播放网| 在线免费观看的www视频| 一夜夜www| 久久精品国产99精品国产亚洲性色| 国产精品电影一区二区三区| 亚洲中文字幕日韩| 一二三四社区在线视频社区8| 免费在线观看黄色视频的| 免费观看精品视频网站| 国产精品亚洲美女久久久| 亚洲 欧美 日韩 在线 免费| 一二三四在线观看免费中文在| 国产精品香港三级国产av潘金莲| 成在线人永久免费视频| 久久久精品国产亚洲av高清涩受| 亚洲 欧美一区二区三区| 少妇熟女aⅴ在线视频| 在线观看美女被高潮喷水网站 | 国产av又大| 狂野欧美激情性xxxx| 午夜福利成人在线免费观看| 制服丝袜大香蕉在线| 国产精品 国内视频| 丰满人妻熟妇乱又伦精品不卡| 在线观看66精品国产| 亚洲国产看品久久| 国产成人影院久久av| 黑人欧美特级aaaaaa片| 搞女人的毛片| 美女午夜性视频免费| 国产亚洲精品久久久久5区| xxxwww97欧美| 可以在线观看毛片的网站| 三级男女做爰猛烈吃奶摸视频| 国产99白浆流出| 99热只有精品国产| 亚洲国产欧美一区二区综合| 可以免费在线观看a视频的电影网站| 国产成人精品久久二区二区免费| 我的老师免费观看完整版| 一二三四社区在线视频社区8| 欧美zozozo另类| 亚洲欧美精品综合久久99| 亚洲自偷自拍图片 自拍| 国产一区二区三区视频了| 日韩欧美三级三区| 成人手机av| 午夜精品一区二区三区免费看| 国语自产精品视频在线第100页| 日韩免费av在线播放| 五月玫瑰六月丁香| 欧美日韩福利视频一区二区| 日韩欧美国产在线观看| 欧美国产日韩亚洲一区| 日本在线视频免费播放| 日本精品一区二区三区蜜桃| 国产一区二区在线av高清观看| 久久久国产成人免费| 怎么达到女性高潮| 好男人电影高清在线观看| 国产欧美日韩一区二区三| 午夜福利在线观看吧| e午夜精品久久久久久久| 波多野结衣巨乳人妻| 91字幕亚洲| 国产一区二区三区在线臀色熟女| 成人亚洲精品av一区二区| 婷婷亚洲欧美| 丰满的人妻完整版| 亚洲五月婷婷丁香| 一级毛片女人18水好多| 老熟妇乱子伦视频在线观看| 精品人妻1区二区| 日韩欧美免费精品| 久9热在线精品视频| 琪琪午夜伦伦电影理论片6080| 变态另类丝袜制服| 在线观看免费日韩欧美大片| 在线播放国产精品三级| 国产亚洲av高清不卡| 成人三级黄色视频| 国产成人精品无人区| 特大巨黑吊av在线直播| 天堂av国产一区二区熟女人妻 | 亚洲五月婷婷丁香| 成人三级做爰电影| 999精品在线视频| 亚洲av熟女| 制服人妻中文乱码| 国内精品一区二区在线观看| 国产精品乱码一区二三区的特点| 伊人久久大香线蕉亚洲五| 欧美黑人欧美精品刺激| 婷婷精品国产亚洲av在线| 悠悠久久av| 国产高清视频在线观看网站| 一本久久中文字幕| 欧美中文综合在线视频| 老司机在亚洲福利影院| 久久久久性生活片| 搡老熟女国产l中国老女人| av中文乱码字幕在线| 舔av片在线| 国产成人啪精品午夜网站| 亚洲国产精品合色在线| 美女午夜性视频免费| 夜夜爽天天搞| 亚洲av成人精品一区久久| 悠悠久久av| 99国产综合亚洲精品| 最新在线观看一区二区三区| 又黄又粗又硬又大视频| 午夜影院日韩av| 免费人成视频x8x8入口观看| 亚洲在线自拍视频| 2021天堂中文幕一二区在线观| 日本免费a在线| 午夜福利成人在线免费观看| 精品不卡国产一区二区三区| av在线播放免费不卡| videosex国产| 香蕉国产在线看| 国产人伦9x9x在线观看| 久久香蕉精品热| 丰满人妻一区二区三区视频av | 女警被强在线播放| 欧美一级a爱片免费观看看 | 99久久无色码亚洲精品果冻| 亚洲avbb在线观看| 久久精品亚洲精品国产色婷小说| 久久精品夜夜夜夜夜久久蜜豆 | 精品少妇一区二区三区视频日本电影| 国产精品亚洲一级av第二区| 国产亚洲精品第一综合不卡| 亚洲九九香蕉| 亚洲人成电影免费在线| АⅤ资源中文在线天堂| 久久中文字幕一级| 可以免费在线观看a视频的电影网站| 中文字幕最新亚洲高清| 午夜福利视频1000在线观看| 国产精品 欧美亚洲| 国产精品1区2区在线观看.| 精华霜和精华液先用哪个| 精品免费久久久久久久清纯| 久久久久国产一级毛片高清牌| 少妇熟女aⅴ在线视频| 久久久国产欧美日韩av| 国产黄色小视频在线观看| 国产成人欧美在线观看| 白带黄色成豆腐渣| 日韩 欧美 亚洲 中文字幕| 免费人成视频x8x8入口观看| 99热这里只有精品一区 | 国产单亲对白刺激| 国产精品99久久99久久久不卡| 免费电影在线观看免费观看| 后天国语完整版免费观看| 窝窝影院91人妻| 黄色女人牲交| 欧美乱妇无乱码| 99国产精品一区二区三区| 久久99热这里只有精品18| 成人手机av| 搞女人的毛片| 欧美黄色片欧美黄色片| av福利片在线| 757午夜福利合集在线观看| 日韩精品免费视频一区二区三区| 亚洲国产精品成人综合色| 亚洲人成网站高清观看| 两个人的视频大全免费| 香蕉丝袜av| 国内精品久久久久精免费| 国产成人系列免费观看| 亚洲成av人片免费观看| 亚洲一区二区三区不卡视频| 美女午夜性视频免费| 欧美日本亚洲视频在线播放| 久久久久久大精品| 精品久久久久久久久久久久久| 国产一级毛片七仙女欲春2| a级毛片a级免费在线| 美女扒开内裤让男人捅视频| 日韩精品中文字幕看吧| 成人一区二区视频在线观看| 久久久久久免费高清国产稀缺| 男女午夜视频在线观看| 久久精品影院6| 黄色片一级片一级黄色片| 看黄色毛片网站| 精品国产亚洲在线| 国产免费av片在线观看野外av| 国产精品av久久久久免费| 真人一进一出gif抽搐免费| 久久 成人 亚洲| 国内揄拍国产精品人妻在线| 欧美乱妇无乱码| 日韩欧美在线乱码| 99re在线观看精品视频| 我要搜黄色片| 色av中文字幕| 又紧又爽又黄一区二区| 天堂√8在线中文| 特大巨黑吊av在线直播| 欧美精品啪啪一区二区三区| 在线观看一区二区三区| 亚洲国产欧美一区二区综合| 亚洲天堂国产精品一区在线| 99久久久亚洲精品蜜臀av| 51午夜福利影视在线观看| 久久久久精品国产欧美久久久| 我的老师免费观看完整版| 欧美一区二区国产精品久久精品 | 久久国产精品人妻蜜桃| 成人特级黄色片久久久久久久| 欧美性猛交黑人性爽| 久久久久国产一级毛片高清牌| 亚洲精品在线美女| 18禁美女被吸乳视频| 在线播放国产精品三级| 精品电影一区二区在线| 国产精品自产拍在线观看55亚洲| 国产区一区二久久| 不卡一级毛片| 久久久精品国产亚洲av高清涩受| 国产精品一区二区三区四区免费观看 | ponron亚洲| 在线观看午夜福利视频| 丁香六月欧美| 亚洲专区中文字幕在线| 亚洲精品中文字幕一二三四区| 级片在线观看| 成人国产一区最新在线观看| 免费观看人在逋| 级片在线观看| 国产不卡一卡二| x7x7x7水蜜桃| 欧美激情久久久久久爽电影| 亚洲成人国产一区在线观看| 精品欧美国产一区二区三| 国产精品野战在线观看| 男人舔奶头视频| 99久久无色码亚洲精品果冻| 国产激情偷乱视频一区二区| 亚洲自拍偷在线| 国产成人av教育| 国产亚洲精品久久久久久毛片| 国产一区在线观看成人免费| 午夜福利在线观看吧| 午夜日韩欧美国产| 亚洲男人天堂网一区| 特大巨黑吊av在线直播| 久久婷婷成人综合色麻豆| 亚洲七黄色美女视频| 亚洲在线自拍视频| 99在线人妻在线中文字幕| 男女那种视频在线观看| 天堂√8在线中文| 黄色毛片三级朝国网站| 国产亚洲欧美在线一区二区| 波多野结衣巨乳人妻| 久久久久久国产a免费观看| 窝窝影院91人妻| 极品教师在线免费播放| 日本熟妇午夜| 精品久久久久久久末码| av福利片在线观看| 久久天躁狠狠躁夜夜2o2o| 777久久人妻少妇嫩草av网站| 亚洲一码二码三码区别大吗| 国内精品一区二区在线观看| 俄罗斯特黄特色一大片| 国产成+人综合+亚洲专区| 久久中文字幕人妻熟女| 搡老熟女国产l中国老女人| 我要搜黄色片| 白带黄色成豆腐渣| 久久久久九九精品影院| 欧美三级亚洲精品| 热99re8久久精品国产| 999久久久国产精品视频| 国产熟女午夜一区二区三区| 三级国产精品欧美在线观看 | 免费人成视频x8x8入口观看| 欧美不卡视频在线免费观看 | 亚洲午夜精品一区,二区,三区| 欧美zozozo另类| 日本成人三级电影网站| 日韩高清综合在线| 日韩欧美 国产精品| av福利片在线| 亚洲国产精品sss在线观看| 99久久综合精品五月天人人| 国产一区在线观看成人免费| 亚洲国产中文字幕在线视频| 国产免费av片在线观看野外av| 国产av一区在线观看免费| 两个人免费观看高清视频| 亚洲国产精品久久男人天堂| 精品国产美女av久久久久小说| 国产精品永久免费网站| 中文字幕人妻丝袜一区二区| 欧美最黄视频在线播放免费| 久久久水蜜桃国产精品网| 久久 成人 亚洲| 免费在线观看完整版高清| 欧美日韩亚洲国产一区二区在线观看| 国内精品久久久久久久电影| 国内精品久久久久精免费| 村上凉子中文字幕在线| 久9热在线精品视频| 色老头精品视频在线观看| 精品国产美女av久久久久小说| 欧美色欧美亚洲另类二区| 999久久久精品免费观看国产| 国产精品av久久久久免费| 亚洲欧美日韩高清在线视频| 久久天堂一区二区三区四区| 欧美中文综合在线视频| 美女午夜性视频免费| 久久精品国产99精品国产亚洲性色| ponron亚洲| 中文字幕精品亚洲无线码一区| 每晚都被弄得嗷嗷叫到高潮| 日本一二三区视频观看| 亚洲精品一卡2卡三卡4卡5卡| 久久久久久久精品吃奶| 老司机深夜福利视频在线观看| 亚洲九九香蕉| 欧美乱色亚洲激情| 欧美成人性av电影在线观看| 欧美性长视频在线观看| 少妇裸体淫交视频免费看高清 | 三级男女做爰猛烈吃奶摸视频| cao死你这个sao货| 亚洲专区国产一区二区| 久久亚洲真实| 一边摸一边做爽爽视频免费| 国产成人影院久久av| 一区二区三区激情视频| 免费在线观看亚洲国产| 男女做爰动态图高潮gif福利片| 男女那种视频在线观看| 欧美一区二区国产精品久久精品 | 嫩草影视91久久| 草草在线视频免费看| 国产精品 国内视频| 在线十欧美十亚洲十日本专区| 国产精品av久久久久免费| 看黄色毛片网站| 一夜夜www| 777久久人妻少妇嫩草av网站| 男女视频在线观看网站免费 | АⅤ资源中文在线天堂| 国内精品久久久久精免费| 十八禁网站免费在线| 两个人看的免费小视频| 亚洲成人国产一区在线观看| 最新美女视频免费是黄的| 一进一出好大好爽视频| 久久午夜综合久久蜜桃| 美女黄网站色视频| 亚洲精品av麻豆狂野| 久久久久久久午夜电影| 亚洲精品av麻豆狂野| 久久久久久国产a免费观看| 成人精品一区二区免费| 中文字幕熟女人妻在线| 国产亚洲精品av在线| 久久中文字幕一级| 手机成人av网站| 国产精华一区二区三区| 国产一级毛片七仙女欲春2| 一本一本综合久久| 91字幕亚洲| 久久久久国产一级毛片高清牌| avwww免费| 中文字幕久久专区| 亚洲中文av在线| 搞女人的毛片| 日韩高清综合在线| 91字幕亚洲| 非洲黑人性xxxx精品又粗又长| 午夜免费成人在线视频| xxxwww97欧美| 国产精品一区二区精品视频观看| 精品久久久久久久末码| 亚洲色图av天堂| 成年人黄色毛片网站| xxx96com| 搡老岳熟女国产| 好男人在线观看高清免费视频| 97碰自拍视频| www.精华液| 男人舔女人下体高潮全视频| 蜜桃久久精品国产亚洲av| 久久天堂一区二区三区四区| 黄色a级毛片大全视频| 午夜福利免费观看在线|