• <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 ?

    Two-dimensional square-Au2S monolayer: A promising thermoelectric material with ultralow lattice thermal conductivity and high power factor*

    2021-07-30 07:42:06WeiZhang張偉XiaoQiangZhang張曉強LeiLiu劉蕾ZhaoQiWang王朝棋andZhiGuoLi李治國
    Chinese Physics B 2021年7期
    關鍵詞:張偉王朝治國

    Wei Zhang(張偉) Xiao-Qiang Zhang(張曉強) Lei Liu(劉蕾)Zhao-Qi Wang(王朝棋) and Zhi-Guo Li(李治國)

    1School of Science,Southwest University of Science and Technology,Mianyang 621010,China

    2Institute of Atomic and Molecular Physics,Sichuan University,Chengdu 610065,China

    3Laboratory for Shock Wave and Detonation Physics,Institute of Fluid Physics,Mianyang 610064,China

    Keywords: first-principles calculations, electron-phonon interactions, lattice thermal conductivity, thermo

    1. Introduction

    Owing to increasingly severe environmental pollution and the depletion of fossil fuels, the search for alternative clean and renewable energy sources is urgent. Thermoelectric(TE)materials can spontaneously convert waste heat into electric energy,so they have great potential applications in alleviating the dilemmas of energy sources.[1-5]The performance of a TE material can be described by the dimensionless figure of meritZT=S2σT/(κl+κe), whereS,σ,T,κl, andκedenote the Seebeck coefficient,electrical conductivity,absolute temperature, lattice thermal conductivity, and electronic thermal conductivity, respectively. High-performance TE materials usually require both high power factor(PF=S2σ)and low total thermal conductivityκ(κ=κl+κe). Consequently, some techniques such as chemical doping,band structure engineering,strain engineering,nano-structuring,and low-dimensional structure were adopted to enhancePFor reduceκ.[6-10]Lowdimensional materials could exhibit significantly higherZTvalues than their bulk counterparts[11,12]due to the decreasedκon account of the phonon boundary scattering and the improvedPFcaused by the quantum confinement effect.

    Recently, the two-dimensional (2D) transition-metal chalcogenidesM2X(M= metal andX= S, Se, Te)have attracted considerable attention due to their nontrivial properties.[13-20]Monolayerδ-Cu2S had an ultralowκlof 0.10 W/mK at 800 K, leading to a highZTof 1.33.[14]TheZTof the metal-shrouded Tl2O monolayer exceeded 3 whenT >700 K.[20]Monolayer Ag2S was also recommended as a promising 2D TE material.[17]Recently, Chenet al.[18]and Wuet al.[19]proposed a new nonmetal-shroudedM2X: monolayer square-Au2S.Its cohesive energy 3.4 eV was comparable to that of monolayer Ge(3.26 eV)and Si(3.98 eV),[21]indicating the possibility to synthesize it experimentally. Chenget al.[18]calculated the lattice thermal conductivity of this monolayer and found that it has an unusually lowκl, but the physical origins behind such a lowκlare unexplored. They also suggested that monolayer square-Au2S has ultrahigh carrier mobilities. However, the carrier mobilities of monolayer square-Au2S calculated by them were very different(their difference was more than 160%), though the same deformation potential theory was used.[22,23]This is due to the fact that the simplified phenomenological model they used contains some tunable parameters, and thus generally lacks sufficient predictive power.[24,25]Therefore, it is necessary to perform the parameter-free first-principles calculations for the electronic transport properties of monolayer square-Au2S to obtain reliable results. Furthermore, we notice that previous work focused only on carrier mobilities,the full thermoelectric transport parameters likeS,σ,κe,andPFfor deriving the figure of meritZTare still lacking.

    In general, the electronic transport properties are computed in terms of the Boltzmann transport equation(BTE) within the constant relaxation time approximation(CRTA).[26-28]Actually, the carrier relaxation time relies on carrier mode, carrier concentration, and temperature.[25]Recently, the electronic transport properties could be accurately predicted by solving the parameter-free BTE under self-energy relaxation time approximation (SERTA) with the scattering limited by the electron-phonon interactions. In addition,as is well known,the spin-orbit coupling(SOC)effect may have a significant influence on the electronic band structure of materials and,further,on electronic transport properties.[29,30]Motivated by the above considerations,in this work,we aim to explore the origin of the lowκlof monolayer square-Au2S and investigate the full TE transport properties together with theZTfrom first-principles calculations and parameter-free BTE.We find that this monolayer possesses a large n-type(p-type)ZT=2.2 (1.5) at 300 K andZT=3.8 (2.5) at 600 K, indicating that it can become a highly promising room-and hightemperature TE material. Furthermore,the effects of EPIs and SOC on TE properties of the monolayer are also discussed.

    2. Computational method

    All first-principles calculations based on density functional theory (DFT) were performed by using the Quantum ESPRESSO package.[31]with Perdew-Burke-Ernzerhof(PBE) exchange-correlation functional.[32]The normconserving pseudopotential[33]was used to describe the corevalence interaction with a plane wave kinetic energy cutoff of 80 Ry (1 Ry=13.6056923(12) eV). The convergence threshold of 1×10-8a.u. (a.u. is short for atomic unit) for total energy and 1×10-5a.u. for forces were used. The DFT-D3 method[34]was used to take into account the long-range van der Waals interaction.The electronic band structures were calculated by the six versions of Heyd-Scuseria-Ernzerh hybrid functional (HSE06). The spin-orbit coupling (SOC) interaction was considered in the calculations of electronic band structure and phonon dispersion. Inab initiomolecular dynamics (AIMD) simulations, a 3×3×1 supercell was used as an initial structure. The timestep and total simulation time were set to be 1 fs and 10 ps,respectively. The lattice thermal conductivity can be obtained by the self-consistent solution of the BTE, as implemented in the ShengBTE package.[35]The 2nd-order interatomic force constants(IFCs)with a 5×5×1q-mesh were calculated by the density functional perturbation theory. A 3×3×1 supercell and 5×5×1k-mesh were used to calculate the 3rd-order anharmonic IFCs, and the interactions up to the eighth nearest-neighbors were included. In the BTE calculations,a denseΓ-centered 50×50×1q-mesh was adopted to obtain converged results. The vacuum lengthLis set to be 20 ?A, which avoids the interactions between layers.For properties requiring volume normalization, an effective thickness of 6.19 ?A was used,which includes the bucking distancehof the monolayer plus twice the van der Waals radius of a sulfur atom.[18,25,27,36,38]

    The EPI matrix elements were computed by using an initial coarse 15×15×1k-mesh with a 5×5×1q-mesh,and then interpolated to a dense 150×150×1k-mesh with a 50×50×1q-mesh using the maximally localized Wannier functions, as implemented in the EPW package.[39,40]These settings are enough to ensure convergence. The energyresolved carrier relaxation time of the electronic state with band indexnand wave vectorkcan be estimated from the imaginary part of the electron self-energy Im(Σ)as follows:

    whereΩBZis the volume of the first Brillouin zone,matrix elementsgmnν(k,q)are the probability amplitude for scattering from an initial electronic state|nk〉into a final state|mk+q〉via a phononqν,fnkis the Fermi-Dirac distribution function,nqνis the Bose-Einstein distribution function,εnkis the electron eigenvalue for the state|nk〉,ωqνis the phonon frequency of wave vectorq, and branch indexν. Then, based on theτnk(E)and band structure from HSE06 with SOC,the electronic transport coefficients,includingS,σ,andκe,can be obtained as follows:

    wheree,Nk,Ω,εF, andvnkrepresent the electron charge,total number ofk-points, volume of the unit cell, Fermi energy, and electron group velocity, respectively. The electronic transport coefficients were solved by using the Boltz-TraP2 package.[27]Hereinafter,we refer to this computational scheme as SOC+SERTA. To elucidate the influence of EPIs on the electronic transport coefficients,the CRTA and SERTA calculations without the SOC were carried out(referred to as NoSOC+CRTA and NoSOC+SERTA hereinafter). The role of the SOC effect is checked by comparing the SOC+SERTA calculations with the NoSOC+SERTA calculations. In the CRTA calculations, the carrier relaxation timeτwas calculated from the equation:τ=μm*/e,where carrier mobilityμand effective massm*were cited from Ref.[18].

    3. Results and discussion

    3.1. Structure of monolayer square-Au2S

    Monolayer square-Au2S has a tetragonal structure with a space group symmetry ofP4/nmm. There are four Au atoms and two S atoms in a unit cell,and the four Au atoms are in a plane. The layer of Au atoms is sandwiched between two layers of S atoms, and each S atom is tetracoordinated with Au atoms as shown in Figs. 1(a) and 1(b). The fully optimized lattice parameter and the bucking distancehof monolayer square-Au2S are 5.74 ?A and 2.59 ?A,respectively. These structural parameters accord well with previous calculations.[19]The phonon dispersion and AIMD simulations indicate that the monolayer square-Au2S possesses good dynamical and thermal stability (see the supplementary material, Fig. S1).Figure 1(c) displays the electron localization functions, from which we can see that the electrons are mostly localized near S atoms,implying the ionic nature of the Au-S bond.In general,weak interatomic bonding is an indicator of lowκl.[7]

    Fig.1. (a)Top view and(b)side view of the atomic structure of monolayer square-Au2S, (c) electron localization functions, and (d) high-symmetry kpoints in the first Brillouin zone.

    3.2. Lattice thermal conductivity

    The calculatedκlversustemperature is displayed in Fig. 2(a). As expected, monolayer square-Au2S has an ultralowκlof 0.72 W/mK at room temperature,which is smaller than other 2D nanosheets have, like SnSe,[41]Bi2Te3,[42]MoS2,[43]BP,[44]PdS2,[3]and comparable to those of the recently reported monolayers Tl2O[13]and Bi2O2Se.[6]The ultralowκlof monolayer square-Au2S is beneficial to the high TE performance. It can also be seen from Fig. 2(a) that theκlof monolayer square-Au2S decreases with temperature increasing, reaching 0.48 W/mK at 600 K. This is mainly due to the inherent enhancement of the phonon-phonon scattering with temperature increasing. It is noted that our calculatedκlof monolayer square-Au2S is lower than that in Ref. [18],which is because the van der Waals interaction exerts influence on group velocity and the phonon relaxation time is included in the present work. The calculated contributions from different phonon branches toκlin Fig. 2(b) reveal that lowfrequency acoustic branches contribute to the majority of theκl. In contrast, the contribution from high-frequency optical branches is quite small.

    According to phonon Boltzmann theory,κlis proportional to the phonon lifetime and the square of the group velocity.[28]Thus, to understand the origin of such an ultralowκl, the phonon group velocities and relaxation timeversusfrequency are shown in Figs. 2(c) and 2(d), respectively. The group velocities and phonon lifetime from the acoustic branches are higher than those from the optical branches, which helps explain why the contribution from acoustic branches accounts for the majority ofκl. The maximum phonon group velocity of all phonon modes for monolayer square-Au2S is quite small(within 3 km/s),resulting in the lowκl. On the other hand, the phonon lifetimes for the acoustic modes are low enough(1 ps-100 ps), which implies the strong phonon scattering. The anharmonic phonon scattering can be characterized by two parameters: the Gr¨uneisen parameterγand the size of the three-phonon scattering phase spaceW. The mode Gr¨uneisen parameter and weighted phase space of three-phonon scattering of the acoustic branches are both large(see Fig.S2 in Supplementary material),leading to low phonon lifetime and,hence,lowκl.

    It is worth noting that EPIs may have an important effect on phonon thermal conductivity.[45,46]However, the present calculations elucidate that the phonon relaxation time arising from the intrinsic phonon-phonon scattering is at least two orders of magnitude smaller than that from electron-phonon scattering (see Fig. S3 in supplementary material). Therefore, according to Matthiessen’s rule,[28]theκlof monolayer square-Au2S due to EPIs can be safely ignored.

    Fig.2. (a)Lattice thermal conductivity κl versus temperature,(b)contribution of phonons at different frequencies to κl,and(c)phonon group velocity,and(d)phonon relaxation time versus frequency at 300 K for monolayer square-Au2S.

    3.3. Electronic transport and TE properties

    Monolayer square-Au2S with lowκlwill be a highly useful TE material if itsSandσare high enough. The electronic transport properties depend mainly on the band structure and carrier relaxation time. We use the hybrid functional HSE06 to overcome the underestimation of bandgap by PBE.As shown in Fig.3(a), monolayer square-Au2S is a semiconductor with a direct bandgap of 0.8 (1.2) eV with (without)SOC,which is slightly smaller than that reported in Ref.[19].The projected density of states shown in Fig. 3(b) indicate that both Au atoms and S atoms contribute to states near the Fermi level, implying that there is a strong hybridization between orbitals of Au and S atoms. Further analyses of the orbital-resolved density of states(see Fig.S4)indicate that the states near the valence band maximum(VBM)are contributed mainly by the hybridization of atomic orbitals of Au atoms and atomic orbitals of S atom. The states around the conduction band minimum (CBM), however, stem mainly from the atomic orbitals of the Au atom. Consequently, the valence band and conduction band may have different dispersion characteristics as shown in Fig.3(a).There exists strong dispersion near the CBM,while the bands around the VBM are relatively flat. Upon the introduction of the SOC effect,the band edges near the VBM become more dispersive,while the band shape around the CBM is hardly affected. Therefore, after including SOC, the band edges around the Fermi level are highly dispersive, leading to small effective mass (m*=0.06mefor electron andm*=0.10mefor hole[19]). According to the deformation potential theory, the carrier mobilityμis inversely proportional to effective massm*. And the electronic conductivityσcan be calculated from the equation:σ=μne,wherenis carrier concentration. Thus,the small effective mass will result in largeμandσ,thereby a high power factor.

    The carrier relaxation time can be accurately calculated from the EPI matrix elements. According to Eq.(1), the carrier relaxation time and EPI matrix elements are related by the electron self-energy Im(Σ). The projections of Im(Σ)on the band structure and the energy-dependent carrier relaxation time are displayed in Figs. 3(a) and 3(c), respectively. States with small Im(Σ)appear around the VBM and CBM because electrons and holes near the band edges are less scattered as a result of the limited phase space.[7,47]Moreover, a strong energy dependence can be witnessed from the energy-dependent carrier relaxation time as shown in Fig.3(c).The carrier relaxation time decreases uniformly with temperature increasing.The relaxation time at 300 K is higher than that at 600 K.This can be easily understood, since more and more phonons are populated with the increase of temperature, which leads the electron-phonon scattering to strengthen.[48]

    Figure 4 shows the curves of electronic transport and TE parametersversuscarrier concentrations at 300 K for n-type and p-type dopings under the SOC+SERTA.Figures 4(a)and 4(b) display the largeSvalues for n-type and p-type doped monolayer square-Au2S.For instance,the absolute value ofSfor n-type(p-type)doping at the optimal carrier concentration(corresponding to the maximumZT)is 265 μV/K(214 μV/K).Both of them are in the range of 200 μV/K-300 μV/K,which is an indicator of good TE material.[1,49]Figures 4(c)and 4(d)show that theσfor n-type doping is superior to that for p-type doping. Notably, the absolute value ofSis inversely proportional to carrier concentration, whereas theσfollows the opposite trend,suggesting that there is a trade-off between them,leading to a maximumPFat a certain carrier concentration.

    Fig. 3. (a) Electronic band structure calculated by HSE06 functional with (solid line) and without considering the SOC effect (gray dotted line), (b)projected density of states with considering SOC effect, and (c) energy-dependent carrier relaxation time τnk(E). Band structure with SOC effect is color-coded according to Im(Σ)at 300 K,which is scaled by color bar with units of eV.

    Fig.4. Curves of electronic transport and TE coefficients versus carrier concentration of n-type(left panels)and p-type(right panels)doped monolayer square-Au2S at 300 K: ((a), (b)) absolute value of Seebeck coefficient S, ((c), (d)) electrical conductivity σ, ((e), (f)) power factor PF, and ((g),(h))figure of merit ZT.

    The calculatedPFvalues in Figs. 4(e) and 4(f) shows that the maximumPFof n-type doping is twice that of p-type doping mainly due to the higherσfor n-type doping. The n-type (p-type) doped monolayer square-Au2S has an exceptionalPF=9.90(4.85) mW/mK2at 300 K, which is higher than that of monolayersδ-Cu2S and Bi2O2Se. The calculatedκefor n-type (p-type) doping at optimal concentration is 0.38 (0.20) W/mK, which is lower thanκl. Moreover, theκefor n-type (p-type) doping contributes only 34% (21%) to the totalκ(see the supplementary material, Fig. S5). Owing to the highPFand quite lowκ, the n-type (p-type)ZTof 2.2(1.5)can be achieved at the optimal hole concentrationnE≈4.0×1010cm-2(nH≈1.1×1011cm-2)andT=300 K as shown in Figs.4(g)and 4(h).

    Figure 5 displays the contour map ofZT versustemperature and doping concentration under SOC+SERTA.It is found that the maximumZTand the optimal carrier concentration both increase with temperature increasing. The maximum ntype (p-type)ZTexceeds 3.7 (2.4) atnE≈8.5×1010cm-2(nH≈4.0×1011cm-2) and 600 K. The maximum n-typeZT= 3.8 is higher than that of typical bulk TE material:SnSe (2.6).[50]and 2D monolayers:δ-Cu2S (1.33),[14]Tl2O(3.35),[20]and Bi2O2Se(3.35).[6]

    Fig.5. Contour map of ZT as a function of temperature and carrier concentration of(a)n-type and(b)p-type doped monolayer square-Au2S.

    3.4. Effects of SOC and EPIs on TE properties

    The SOC effect and EPIs may play a vital role in determining the electronic properties of materials.[25,30,51,52]The influence of the SOC effect can be revealed by comparing the results from SOC+SERTA and NoSOC+SERTA calculations as shown in Fig. 4. With the consideration of SOC, for ptype doping,Sdecreases whereasσincreases significantly,which can be understood through the above analyses of band structures. Since the increase ofσis dominant,the maximumPFandZTwith SOC are~4 times and~3.5 times larger than the results without SOC,respectively. Moreover,the optimum hole concentration decreases by nearly two orders of magnitude with SOC strengthening. On the other hand, the band edges around CBM are less affected by the SOC effect as shown in Fig. 3(a). Therefore, forSandσof n-type doping, the difference between the results with and without the SOC effect is much smaller than the counterparts in the case of p-type doping. Moreover, the maximum values of n-typePFandZTwith and without the SOC effect are close to each other(see the left panel of Fig.4).

    To reveal the influence of EPIs on the electronic transport properties, we compare the results from SERTA and CRTA calculations in Fig. 4. For n-type and p-type dopings, theSfrom SERTA reasonably accords with that from CRTA,which indicates the low correlation betweenSand carrier relaxation time. The discrepancy between the CRTA and SERTA results is apparent forσ,κe,and the maximum values ofPFandZT,which are shown in Fig. 4 and Fig. S5. The maximum values ofPF(ZT) from SERTA are~56% (28%) and~90%(84%)lower than those from CRTA for n-type and p-type dopings,respectively. Therefore,the strong energy dependence ofτnk(E)plays an essential role in determining the overall electronic transport and TE performance.The completely different treatment of carrier relaxation time is responsible for the discrepancy.In the CRTA calculations,the carrier relaxation time is regarded as a constant. It is calculated by the deformation potential theory, which only considers the electron-acoustic phonon scattering. However,for monolayer square-Au2S,the optical phonon scattering is comparable to that from the acoustic phonon branches (see Fig. S6 in the supplementary material). The SERTA adopts the energy-resolved carrier relaxation time deduced from the EPI matrix elements which take into account all electron-phonon scattering processes.To date,the electronic transport and TE properties of several materials,including Li,[53]Si,[29,30]GaAs,[29]SnSe,[52]Mg3Sb2,[24]CoSi,[51]etc. have been investigated by the parameter-free algorithm and the calculation results accord well with the experimental data. Therefore,the electronic transport and TE properties of monolayer square-Au2S obtained by the SERTA are believed to be more predictive than by the CRTA,although the corresponding experimental data are not available at present.In addition,although the maximum values ofPFandZTfrom the SERTA seriously deviate from those from the CRTA, the optimum carrier concentrations predicted by the two methods are relatively close to each other.

    4. Conclusions

    In summary, thermal, electronic transport, and thermoelectric properties of monolayer square-Au2S are systematically investigated via a parameter-freeab initioBoltzmann transport algorithm. Owing to the low group velocity and strong anharmonic phonon scattering, the monolayer square-Au2S possesses an ultralow lattice thermal conductivityκlof 0.72 W/mK at 300 K. The square-Au2S monolayer has extraordinarily high Seebeck coefficient and electrical conductivity. Consequently, the maximum power factor of the ntype(p-type)square-Au2S monolayer can be as large as 9.90(4.85)mW/mK2at 300 K.Benefiting from the ultralowκland the high power factor,a high room-temperature figure of meritZTof 2.2(1.5)can be achieved for n-type(p-type)doping,and it increases up to an ultrahigh value of 3.8 (2.5) at 600 K. In addition,when EPIs are considered,theZTvalues are significantly reduced by 28%(84%)for n-type(p-type)doping. After introducing the SOC effect, the p-typeZTis substantially increased by 3.5 times but the n-type one is almost unaffected.Our analyses strongly suggest that the 2D square-Au2S monolayer could be a potential candidate for future-generation TE applications.

    Acknowledgment

    The calculations were carried out on TianHe-2 at the LvLiang Cloud Computing Center in China.

    猜你喜歡
    張偉王朝治國
    正確看待輸和贏
    A MULTIPLE q-EXPONENTIAL DIFFERENTIAL OPERATIONAL IDENTITY?
    巍治國藝術作品欣賞
    昨天 今天
    金秋(2020年14期)2020-10-28 04:15:40
    藝術百家:張偉 何是雯
    電影文學(2018年10期)2018-12-10 00:48:32
    看得到的轉變
    中華家教(2018年9期)2018-10-19 09:30:00
    養(yǎng)心殿,帶你走進大清王朝的興衰沉浮
    金橋(2018年10期)2018-10-09 07:27:44
    數(shù)學潛能知識月月賽
    略論古齊國的治國之道
    王朝梁研究員
    少妇的丰满在线观看| 国产男女内射视频| 久久青草综合色| 汤姆久久久久久久影院中文字幕| 天天操日日干夜夜撸| 狠狠婷婷综合久久久久久88av| 久久亚洲国产成人精品v| 日韩 欧美 亚洲 中文字幕| 久久久国产欧美日韩av| 男人操女人黄网站| 免费在线观看黄色视频的| 亚洲精品美女久久久久99蜜臀 | 看十八女毛片水多多多| 人人妻人人爽人人添夜夜欢视频| 日韩,欧美,国产一区二区三区| 国产精品麻豆人妻色哟哟久久| 日韩精品免费视频一区二区三区| 一级a爱视频在线免费观看| 亚洲精品一二三| 手机成人av网站| 国产片特级美女逼逼视频| 亚洲自偷自拍图片 自拍| 久久国产亚洲av麻豆专区| 久久久久网色| 飞空精品影院首页| av在线老鸭窝| h视频一区二区三区| 91成人精品电影| 少妇精品久久久久久久| 美女中出高潮动态图| 日韩 欧美 亚洲 中文字幕| 亚洲精品美女久久久久99蜜臀 | 国产亚洲欧美精品永久| 精品一区二区三区四区五区乱码 | 人人澡人人妻人| 高清av免费在线| 久久久亚洲精品成人影院| 亚洲av电影在线进入| 亚洲成人国产一区在线观看 | 亚洲美女黄色视频免费看| 色精品久久人妻99蜜桃| a级毛片在线看网站| 国产黄色免费在线视频| videosex国产| 在线天堂中文资源库| 亚洲成av片中文字幕在线观看| 久久久久久久大尺度免费视频| 一个人免费看片子| 一二三四社区在线视频社区8| 精品免费久久久久久久清纯 | 国产精品欧美亚洲77777| 精品久久久精品久久久| 三上悠亚av全集在线观看| 亚洲人成网站在线观看播放| 你懂的网址亚洲精品在线观看| 欧美精品一区二区免费开放| 大片电影免费在线观看免费| 丁香六月欧美| 国产老妇伦熟女老妇高清| 精品国产超薄肉色丝袜足j| 涩涩av久久男人的天堂| 午夜影院在线不卡| 巨乳人妻的诱惑在线观看| 国产av一区二区精品久久| 欧美激情极品国产一区二区三区| 亚洲国产日韩一区二区| 国产免费现黄频在线看| 精品国产一区二区三区久久久樱花| 亚洲av日韩精品久久久久久密 | 肉色欧美久久久久久久蜜桃| 亚洲欧美精品自产自拍| 午夜免费男女啪啪视频观看| 亚洲成人国产一区在线观看 | 亚洲精品国产一区二区精华液| 久久久久视频综合| 99精品久久久久人妻精品| 国产在线视频一区二区| 91精品三级在线观看| 国产一区二区三区综合在线观看| 日韩av不卡免费在线播放| 久久久久久久久久久久大奶| 交换朋友夫妻互换小说| 国产熟女欧美一区二区| 一级毛片黄色毛片免费观看视频| 久久亚洲精品不卡| 亚洲少妇的诱惑av| 亚洲中文字幕日韩| 国产精品99久久99久久久不卡| 不卡av一区二区三区| 国产精品偷伦视频观看了| 免费在线观看黄色视频的| 亚洲色图 男人天堂 中文字幕| 国产黄色免费在线视频| 99精国产麻豆久久婷婷| 国产高清不卡午夜福利| 日韩精品免费视频一区二区三区| 日本91视频免费播放| 人妻 亚洲 视频| 亚洲精品久久成人aⅴ小说| 人人妻,人人澡人人爽秒播 | 香蕉丝袜av| 天堂中文最新版在线下载| 欧美日韩综合久久久久久| 波野结衣二区三区在线| 狠狠婷婷综合久久久久久88av| 亚洲黑人精品在线| 精品福利永久在线观看| 久久人妻福利社区极品人妻图片 | 在线观看国产h片| 国产精品欧美亚洲77777| 爱豆传媒免费全集在线观看| 精品少妇黑人巨大在线播放| 丝袜在线中文字幕| 最近手机中文字幕大全| 免费久久久久久久精品成人欧美视频| 国产黄频视频在线观看| 久久天躁狠狠躁夜夜2o2o | 一本大道久久a久久精品| 国产精品免费视频内射| 一级毛片我不卡| 少妇猛男粗大的猛烈进出视频| 午夜福利视频精品| 国产片特级美女逼逼视频| 国产亚洲av高清不卡| 午夜精品国产一区二区电影| 中文字幕制服av| 精品国产一区二区三区四区第35| 赤兔流量卡办理| 日本黄色日本黄色录像| 国产伦人伦偷精品视频| 国产黄频视频在线观看| av福利片在线| 国产一区二区在线观看av| 成年女人毛片免费观看观看9 | 欧美日韩成人在线一区二区| 午夜老司机福利片| 欧美中文综合在线视频| 国产精品欧美亚洲77777| 亚洲 欧美一区二区三区| 高清不卡的av网站| 国产一区二区 视频在线| 亚洲欧洲精品一区二区精品久久久| 亚洲av电影在线观看一区二区三区| 久久精品久久精品一区二区三区| 亚洲av片天天在线观看| 老司机亚洲免费影院| 亚洲专区中文字幕在线| 一个人免费看片子| 一二三四社区在线视频社区8| 精品国产乱码久久久久久男人| 国产精品av久久久久免费| 汤姆久久久久久久影院中文字幕| 欧美日韩福利视频一区二区| 午夜久久久在线观看| 99久久综合免费| 国产精品一二三区在线看| 999久久久国产精品视频| 99re6热这里在线精品视频| 亚洲一区二区三区欧美精品| 精品熟女少妇八av免费久了| 一本色道久久久久久精品综合| 搡老乐熟女国产| 丰满少妇做爰视频| 91字幕亚洲| 久久精品熟女亚洲av麻豆精品| 在线天堂中文资源库| 久久九九热精品免费| 欧美久久黑人一区二区| 亚洲精品成人av观看孕妇| 亚洲成人免费av在线播放| 亚洲av美国av| 成在线人永久免费视频| 国产黄频视频在线观看| 女警被强在线播放| 日日爽夜夜爽网站| 国产欧美日韩一区二区三区在线| 国产不卡av网站在线观看| 肉色欧美久久久久久久蜜桃| 久久性视频一级片| 亚洲精品国产一区二区精华液| 夜夜骑夜夜射夜夜干| 丝袜喷水一区| 国产精品九九99| 成人手机av| 久久久久国产一级毛片高清牌| 国产亚洲精品第一综合不卡| 啦啦啦 在线观看视频| 国产黄频视频在线观看| av在线播放精品| 悠悠久久av| 老汉色av国产亚洲站长工具| 精品熟女少妇八av免费久了| 国产免费视频播放在线视频| 日本五十路高清| 女人久久www免费人成看片| 亚洲五月婷婷丁香| 99热网站在线观看| 成人18禁高潮啪啪吃奶动态图| 亚洲av片天天在线观看| 久久久久久久大尺度免费视频| 黄片小视频在线播放| 男女免费视频国产| 在线观看免费高清a一片| 国产野战对白在线观看| 69精品国产乱码久久久| 亚洲精品第二区| 亚洲av电影在线进入| 久久久久精品国产欧美久久久 | 国产精品久久久久成人av| 亚洲,欧美精品.| 少妇人妻久久综合中文| 欧美亚洲日本最大视频资源| 99国产精品一区二区蜜桃av | 久久精品国产亚洲av高清一级| 两个人看的免费小视频| 丝袜喷水一区| 精品国产一区二区久久| 99热全是精品| 国产福利在线免费观看视频| 精品卡一卡二卡四卡免费| av视频免费观看在线观看| 亚洲伊人久久精品综合| 99热全是精品| 肉色欧美久久久久久久蜜桃| 男男h啪啪无遮挡| 欧美av亚洲av综合av国产av| 男女午夜视频在线观看| 两人在一起打扑克的视频| 亚洲国产精品一区三区| 啦啦啦中文免费视频观看日本| 亚洲专区国产一区二区| 亚洲男人天堂网一区| 亚洲av国产av综合av卡| 久久久精品国产亚洲av高清涩受| 夫妻午夜视频| 国产一级毛片在线| 美女脱内裤让男人舔精品视频| 国产成人欧美在线观看 | 黄色毛片三级朝国网站| 十八禁高潮呻吟视频| 国产av精品麻豆| 国产精品亚洲av一区麻豆| 久久精品亚洲熟妇少妇任你| 少妇被粗大的猛进出69影院| 中国美女看黄片| 久久久久视频综合| 日韩一区二区三区影片| 久久亚洲国产成人精品v| 国产黄色免费在线视频| 精品一区二区三区av网在线观看 | 侵犯人妻中文字幕一二三四区| 午夜影院在线不卡| 免费观看人在逋| 久久久久视频综合| 在线 av 中文字幕| 久久精品aⅴ一区二区三区四区| 久久精品国产亚洲av高清一级| 亚洲国产av新网站| 午夜免费鲁丝| 国产精品免费视频内射| av欧美777| 人成视频在线观看免费观看| 欧美中文综合在线视频| 久久久久网色| 国产主播在线观看一区二区 | 久久青草综合色| 精品国产国语对白av| 国产一区有黄有色的免费视频| 亚洲av美国av| 中国美女看黄片| 久久久久精品国产欧美久久久 | 91精品国产国语对白视频| 999精品在线视频| 欧美+亚洲+日韩+国产| 人妻一区二区av| 国产国语露脸激情在线看| www.精华液| 人人妻人人添人人爽欧美一区卜| 亚洲 国产 在线| 欧美老熟妇乱子伦牲交| 亚洲国产精品一区二区三区在线| 国产精品成人在线| 两个人看的免费小视频| 男男h啪啪无遮挡| 婷婷成人精品国产| 国产男女超爽视频在线观看| 中文字幕色久视频| 久久国产亚洲av麻豆专区| 老汉色∧v一级毛片| 视频区欧美日本亚洲| 少妇人妻久久综合中文| 在线观看免费高清a一片| 精品人妻1区二区| 亚洲欧美精品自产自拍| 国产精品欧美亚洲77777| 国产精品国产三级国产专区5o| 18禁国产床啪视频网站| 如日韩欧美国产精品一区二区三区| 精品一区二区三区av网在线观看 | 久久久精品区二区三区| 亚洲人成网站在线观看播放| 免费女性裸体啪啪无遮挡网站| 欧美日韩亚洲国产一区二区在线观看 | 国语对白做爰xxxⅹ性视频网站| 久久精品熟女亚洲av麻豆精品| 青草久久国产| 国产成人a∨麻豆精品| 又紧又爽又黄一区二区| 另类亚洲欧美激情| 男女边摸边吃奶| 少妇猛男粗大的猛烈进出视频| 亚洲第一av免费看| 超色免费av| 亚洲 欧美一区二区三区| 久久国产精品男人的天堂亚洲| 日本av免费视频播放| 欧美乱码精品一区二区三区| 国产不卡av网站在线观看| 成年人黄色毛片网站| netflix在线观看网站| 欧美黑人精品巨大| 国产免费福利视频在线观看| 黄色怎么调成土黄色| 欧美精品高潮呻吟av久久| 美女脱内裤让男人舔精品视频| 国产精品欧美亚洲77777| 99热全是精品| 免费观看人在逋| 青春草亚洲视频在线观看| 午夜精品国产一区二区电影| 国产男女超爽视频在线观看| 久久ye,这里只有精品| 乱人伦中国视频| 超色免费av| 国产精品熟女久久久久浪| 国产欧美日韩精品亚洲av| 黑人猛操日本美女一级片| 麻豆乱淫一区二区| 国产熟女欧美一区二区| 久久午夜综合久久蜜桃| 少妇精品久久久久久久| 麻豆av在线久日| 亚洲欧美清纯卡通| 国产精品三级大全| 国产老妇伦熟女老妇高清| 成年人免费黄色播放视频| 一级毛片电影观看| 纯流量卡能插随身wifi吗| 美女脱内裤让男人舔精品视频| 丰满人妻熟妇乱又伦精品不卡| 欧美日韩亚洲高清精品| 久久中文字幕一级| 丁香六月欧美| 久久毛片免费看一区二区三区| 十分钟在线观看高清视频www| 超碰97精品在线观看| 日本a在线网址| 爱豆传媒免费全集在线观看| 国产高清国产精品国产三级| 丝瓜视频免费看黄片| 日本a在线网址| 七月丁香在线播放| 久久国产精品影院| 大陆偷拍与自拍| 大码成人一级视频| 亚洲国产精品成人久久小说| 国产亚洲av片在线观看秒播厂| 99国产精品一区二区蜜桃av | 国产男人的电影天堂91| 国产精品熟女久久久久浪| 国产精品久久久人人做人人爽| 99热网站在线观看| 国产成人av教育| 侵犯人妻中文字幕一二三四区| 一本大道久久a久久精品| 赤兔流量卡办理| 婷婷色综合大香蕉| 欧美精品啪啪一区二区三区 | 真人做人爱边吃奶动态| 国产精品香港三级国产av潘金莲 | 国产无遮挡羞羞视频在线观看| 国产免费现黄频在线看| 久久久久精品国产欧美久久久 | 国产精品熟女久久久久浪| 亚洲人成77777在线视频| 午夜91福利影院| 一级毛片黄色毛片免费观看视频| 不卡av一区二区三区| 满18在线观看网站| 黄色视频在线播放观看不卡| 欧美亚洲 丝袜 人妻 在线| 又紧又爽又黄一区二区| 国产精品一国产av| 成年av动漫网址| 国产成人av教育| 午夜免费成人在线视频| 91麻豆av在线| 国产精品国产av在线观看| 亚洲av电影在线观看一区二区三区| 久久av网站| 欧美日韩视频高清一区二区三区二| 国产精品国产av在线观看| 制服人妻中文乱码| 日本黄色日本黄色录像| 在线观看免费高清a一片| 国产男女超爽视频在线观看| 免费日韩欧美在线观看| 亚洲激情五月婷婷啪啪| 999精品在线视频| 久久精品久久久久久噜噜老黄| 99久久人妻综合| 性少妇av在线| 日韩电影二区| 黑人欧美特级aaaaaa片| 美女午夜性视频免费| 国产欧美日韩综合在线一区二区| 亚洲熟女毛片儿| 只有这里有精品99| 晚上一个人看的免费电影| 美女主播在线视频| 女人高潮潮喷娇喘18禁视频| 久久久久国产一级毛片高清牌| 在线观看免费视频网站a站| 伦理电影免费视频| 看免费成人av毛片| 精品国产一区二区三区久久久樱花| 午夜福利视频精品| 欧美激情高清一区二区三区| 97人妻天天添夜夜摸| 亚洲黑人精品在线| 啦啦啦啦在线视频资源| 一区二区av电影网| 搡老岳熟女国产| 欧美日韩亚洲国产一区二区在线观看 | 精品一区二区三卡| √禁漫天堂资源中文www| 午夜福利一区二区在线看| 亚洲欧洲精品一区二区精品久久久| 一本一本久久a久久精品综合妖精| 精品少妇久久久久久888优播| www.av在线官网国产| 精品少妇内射三级| 国产成人精品无人区| 国产亚洲av高清不卡| 一区在线观看完整版| 91字幕亚洲| e午夜精品久久久久久久| tube8黄色片| 夫妻午夜视频| 国产一区二区三区综合在线观看| 王馨瑶露胸无遮挡在线观看| 亚洲av日韩在线播放| 老司机在亚洲福利影院| 国产成人影院久久av| 欧美亚洲日本最大视频资源| 一级毛片 在线播放| 日韩精品免费视频一区二区三区| 亚洲av电影在线观看一区二区三区| 久久鲁丝午夜福利片| 精品久久久精品久久久| 男女边摸边吃奶| 欧美亚洲日本最大视频资源| 桃花免费在线播放| 久热这里只有精品99| 亚洲欧美日韩高清在线视频 | 欧美激情 高清一区二区三区| 精品少妇久久久久久888优播| 老司机影院毛片| a级毛片黄视频| 国产黄频视频在线观看| 精品人妻1区二区| 婷婷丁香在线五月| 18禁国产床啪视频网站| 精品高清国产在线一区| 性色av乱码一区二区三区2| 久久久久国产精品人妻一区二区| 亚洲人成电影免费在线| 国产免费又黄又爽又色| 我的亚洲天堂| 中文字幕另类日韩欧美亚洲嫩草| 亚洲精品一卡2卡三卡4卡5卡 | 一本—道久久a久久精品蜜桃钙片| 日韩精品免费视频一区二区三区| 天堂8中文在线网| 两个人免费观看高清视频| 极品人妻少妇av视频| 韩国高清视频一区二区三区| 成人亚洲精品一区在线观看| 亚洲激情五月婷婷啪啪| 别揉我奶头~嗯~啊~动态视频 | 亚洲欧美一区二区三区国产| 亚洲成色77777| 黑人欧美特级aaaaaa片| 午夜福利一区二区在线看| 一本—道久久a久久精品蜜桃钙片| 亚洲专区中文字幕在线| 丝袜人妻中文字幕| 中文乱码字字幕精品一区二区三区| 久久精品人人爽人人爽视色| 久久综合国产亚洲精品| 午夜福利乱码中文字幕| 国产精品一国产av| 欧美日韩国产mv在线观看视频| kizo精华| 少妇人妻久久综合中文| 精品国产超薄肉色丝袜足j| 亚洲欧美精品自产自拍| 91九色精品人成在线观看| 亚洲中文av在线| 亚洲国产中文字幕在线视频| av线在线观看网站| 国产亚洲精品久久久久5区| 午夜激情久久久久久久| 中文字幕亚洲精品专区| 超色免费av| 女性被躁到高潮视频| 亚洲av日韩精品久久久久久密 | 亚洲成人手机| www.999成人在线观看| 久久久精品94久久精品| 在线观看人妻少妇| 亚洲人成电影免费在线| 国产一级毛片在线| 国产精品一国产av| 麻豆乱淫一区二区| 日韩av在线免费看完整版不卡| 婷婷色综合www| 大香蕉久久网| 久久青草综合色| 亚洲久久久国产精品| 国产视频首页在线观看| 成人午夜精彩视频在线观看| 国产亚洲欧美精品永久| 午夜影院在线不卡| 爱豆传媒免费全集在线观看| 国产精品麻豆人妻色哟哟久久| bbb黄色大片| 亚洲国产成人一精品久久久| 操出白浆在线播放| 亚洲专区中文字幕在线| 精品熟女少妇八av免费久了| 国产爽快片一区二区三区| 中文字幕人妻熟女乱码| 亚洲精品国产区一区二| 天天躁夜夜躁狠狠久久av| 亚洲中文字幕日韩| 各种免费的搞黄视频| 欧美人与善性xxx| 午夜91福利影院| 免费高清在线观看视频在线观看| 人人妻,人人澡人人爽秒播 | 丁香六月天网| 精品一区二区三区av网在线观看 | 一区福利在线观看| 在线观看免费高清a一片| 一级,二级,三级黄色视频| 亚洲图色成人| 久久久久精品国产欧美久久久 | 欧美精品一区二区大全| 91字幕亚洲| www.精华液| 女性生殖器流出的白浆| 水蜜桃什么品种好| 日本vs欧美在线观看视频| 国产91精品成人一区二区三区 | 午夜福利视频精品| 久久精品成人免费网站| 新久久久久国产一级毛片| 久久热在线av| 男女免费视频国产| 亚洲精品中文字幕在线视频| 大码成人一级视频| 日韩精品免费视频一区二区三区| 国产成人欧美在线观看 | 日本五十路高清| 成年女人毛片免费观看观看9 | 亚洲欧美精品综合一区二区三区| 51午夜福利影视在线观看| 9191精品国产免费久久| 大陆偷拍与自拍| 免费在线观看视频国产中文字幕亚洲 | 黄色片一级片一级黄色片| 亚洲国产最新在线播放| 黄色一级大片看看| 免费在线观看日本一区| www.999成人在线观看| 国产男人的电影天堂91| 亚洲伊人色综图| 大香蕉久久成人网| 少妇 在线观看| 天天躁夜夜躁狠狠久久av| 亚洲一区中文字幕在线| 国产有黄有色有爽视频| 久久久久久久精品精品| 久久天堂一区二区三区四区| av天堂久久9| 国产精品.久久久| 亚洲自偷自拍图片 自拍| 麻豆av在线久日| 三上悠亚av全集在线观看| 一级片'在线观看视频| 亚洲男人天堂网一区| 国产激情久久老熟女| 啦啦啦 在线观看视频| 又黄又粗又硬又大视频| 18在线观看网站| 伊人久久大香线蕉亚洲五| 大片电影免费在线观看免费| 欧美激情 高清一区二区三区| 黄色毛片三级朝国网站| 精品免费久久久久久久清纯 | 国产淫语在线视频| 搡老乐熟女国产| 亚洲av日韩精品久久久久久密 | 亚洲精品一区蜜桃|