• <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 ?

    First principles study of behavior of helium at Fe(110)–graphene interface?

    2021-05-06 08:56:26YanMeiJing荊艷梅andShaoSongHuang黃紹松
    Chinese Physics B 2021年4期

    Yan-Mei Jing(荊艷梅) and Shao-Song Huang(黃紹松)

    Key Laboratory of Material Modification by Laser,Ion and Electron Beams(Dalian University of Technology),Ministry of Education,Dalian 116024,China

    Keywords: Fe(110)–graphene,helium,interface,first principles calculations

    1. Introduction

    With the rapid development of advanced nuclear energy systems, the need for the development and application of structural materials with higher radiation tolerance has increased.[1]Point defects (vacancies and interstitials) generated by high-energy neutrons can evolve into extended defects such as voids and interstitial clusters within the structural materials at elevated temperatures. In addition,a certain number of helium (He) are produced by the (n, α) transmutation reaction.[2]Owing to the low solubility of He atoms,their diffusion and aggregation results in the precipitation and nucleation of He bubbles.[3]The synergistic interaction of these defects leads the mechanical properties of the structural material to degrade.[4–10]Increasing the fraction of interface/boundaries in materials is an important strategy to enhance the irradiation effect tolerance by providing more defect recommendation sites.[11–14]In particular,multilayer metallic systems such as W/Cu,[15]Cu/Nb,[16]and Cu/V[17]systems have been studied extensively as structural materials for mitigating radiation damage.

    Further, graphene has attracted much attention due to its highly dense interface,[18–20]with a two-dimensional structure packed by a single layer of C atoms. Several studies reported their results on the radiation damage resistance of copper–graphene, nickel–graphene, and vanadium–graphene nanocomposites through molecular dynamics and experiments,[21–23]it was found that the metal–graphene nanocomposite had less defects remaining in the bulk region after collision cascades, illustrating the self-healing performance. However, the atomic mechanism was still unknown,especially for the interaction between the graphene and metal substrates. Furthermore, as is well known, stainless steels, in which Fe is the basic element in the matrix (with more than 80 wt%),are the most commonly constructive and prospective materials in nuclear systems. As stated, He is an important product of neutron transmutation,affecting many of the properties of structural materials with point defects.[24–29]Thus,previous studies promoted us to figure out whether the Fe–graphene interface can affect the behaviors of intrinsic defects and act as a good He permeation barrier. In this study, we aim to investigate the potential usage of steel–graphene with multiply interface structures for tolerating the radiation damage. Therefore, using ab initio calculations, we investigate the energetical stability of the Fe–graphene system, the formation of the intrinsic defects, and the behaviors of an interstitial He atom. The rest of this paper is organized as follows.The method of first-principles calculations, and calculational equations are presented in Section 2. In Section 3,the results of the behaviors of the intrinsic defects, and He atoms in the Fe(110)–graphene system are discussed. The major findings are summarized in Section 4.

    2. Computational method

    where Etotal,Esub,and Egare the energy of the composite system, standalone substrate, and graphene, respectively, and Ncis the number of C atoms in the graphene sheet.

    The binding energy of two defects, A and B, in the Fe(110)–graphene system is given by[45]

    Here, E(A) or E(B) is the total energy of a single defect in the structure, E(AB) is the total energy of a supercell with two defects, and E(perfect) is the total energy of the prefect structure without any defects. Following this convention, the positive binding energy corresponds to exothermic defect formation reaction,implying an attractive interaction between A and B.

    The formation energy of a single vacancy or an interstitial atom(Ef)in the Fe(110)–graphene structure is defined as

    where E(defect) and E(perfect) are the total energy of the Fe(110)–graphene system with and without a point defect,respectively; E(Fe)represents the cohesive energy per Fe atom in bcc Fe, E(C) denotes the energy per C atom in graphene;E(He) is the energy of an isolated He atom; m=1, n=0 ,and p=0 for an Fe vacancy in the Fe layer;m=0,n=1,and p=0 for a C vacancy in the graphene layer;m=?1,n=0,and p=0 for an Fe interstitial atom;m=0,n=?1,and p=0 for a C interstitial atom;m=0,n=0,and p=?1 for an He interstitial atom.

    3. Results and discussion

    3.1. Structure and bonding properties

    Figure 1 shows the structure of the Fe(110)–graphene interface; a Moir′e pattern forms in the Fe(110)–graphene, with a large corrugation of the graphene layer. Owing to the lattice mismatch between the Fe substrate and graphene,C atoms occupy various adsorption sites on the Fe substrate.[46]The results indicate that the interaction between the Fe substrate and graphene is strong. In this case, it is vital to investigate the equilibrium binding distance and binding energy of the Fe(110)–graphene system.According to the equilibrium binding distance, the interaction between graphene and the substrate can be divided into two classes:[41]one is represented by an equilibrium binding distance,d of ≤2.3 ?A which indicates strong interaction or chemisorption, and the other belongs in weak interaction or physisorption. According to Eq. (1), the binding energy of the Fe(110)–graphene structure is 0.05 eV/C and the binding distance is ~2.13 ?A while the previously reported experimental and theoretical value are ~2.09 ?A and 2.10 ?A respectively.[39,47]From the energy and distance viewpoint, the binding between the Fe substrate and graphene is strong. The graphene layer on the Fe(110)substrate exhibits a similar binding behavior to that observed on other metal substrates such as Ni,Co,and Pd.[48–50]

    The total density of states (TDOS) of the Fe(110)–graphene system and local density of states(LDOS)between graphene and the topmost Fe layer are shown in Fig.2.The Fed orbital significantly affects the TDOS near the Fermi level.Thus, the metal substrate determines the Fermi level of the composite material. The strong hybridization of the Fe-d state and C-p state in the LDOS indicates that a strong covalent bond forms between the Fe atom and C atom, similar to the previously reported cases of graphene on Rh(111)[51]and Ni(111).[52]The small interfacial distance can result in the overlap of the wave functions of the d electrons of the metal and p electrons of graphene,leading to orbital hybridization.

    Fig.1. Structure of Fe(110)–graphene system,showing(a)top view and(b)side view of structure,with purple and gray balls representing Fe atom and C atom,respectively.

    Fig.2. (a)Total density of states(TDOS)of Fe(110)–graphene system and(b) local density of states (LDOS) between graphene and the topmost Fe layer,with colored solid lines showing projected DOS from s,p,d orbitals,respectively.

    Weser et al.[53]and Dedkov et al.[54]reported a magnetic moment of approximately 0.05μB–0.1μBper carbon atom for the C atoms of a graphene layer contacting a ferromagnetic Ni(111) substrate. In this work, the magnetic moment of C1was found to be ?0.036μB,which forms an antiferromagnetic couple with the nearest Fe atom. On the other hand,the magnetic moment of the C2atom was approximately+0.022 μB.This result is consistent with that reported by Liu et al.[47]The magnetic moments of C atoms in Fe(110)–graphene are attributed to the Fe3d–C2p orbital hybridization.

    Fig.3. Differential charge density of Fe(110)–graphene interface region(isovalue: 0.005 e/?A3),showing(a)side view and(b)top view of interface,where big and small balls represent Fe and C atoms,respectively,blue contour denotes electron depletion region,and yellow contour refers to electron accumulation region.

    Fig.4. Interlayer charge difference in Fe(110)–graphene interface region(?ρ = ρinterface ?ρFe ?ρC). Area between red line and 0 line displays the value of electron depletion or accumulation. Value at interface around 10.43 ?A

    3.2. Formation and stability of intrinsic defects

    The formation energy values of single vacancies of the C and Fe atoms in different layers in Fe(110)–graphene are calculated, and the results are listed in Table 1. The formation energy of the C vacancy in a single graphene layer is also calculated. The single graphene layer is obtained by removing all the Fe atoms in the Fe(110)–graphene system. That is,the single graphene layer is the same as the graphene layer in the Fe(110)–graphene in terms of the initial size and shape. The C vacancy formation energy in the single graphene layer is 8.09 eV,in agreement with previously calculated results.[55,56]However, it is slightly larger than the experiment value of 7.0±0.5 eV.[15]The C vacancy formation energy values of the two types of C atoms(i.e.,C1atom and C2atom)in Fe(110)–graphene are 1.94 eV and 1.97 eV, respectively, which are lower than those for the single graphene layer. This indicates that the C vacancy prefers to form in Fe(110)–graphene. The result is consistent with that reported for Cu/graphene/Cu.[56]The hybridization of C atoms in graphene changes from sp2to sp3due to its interaction with the metal. Consequently,the strength of the in-plane C–C bond is weakened.[57]The formation energy of the Fe vacancy increases with the number of Fe layers increasing. The formation energy of the Fe vacancy in the third layer is close to that in bulk Fe(~2.17 eV).Hence,it is reasonable for us to fix the three bottom Fe layers. The Fe vacancy formation energy for the topmost layer is lower than those for the other layers and bulk Fe, indicating that Fe vacancies prefer to form at the interface rather than stay in bulk Fe. This phenomenon can be attributed to the fact that the interaction between Fe and graphene is weaker than the binding of Fe–Fe in bulk Fe.

    Table 1. Formation energy values of C vacancies and Fe vacancies in Fe(110)–graphene system. The abbreviations: 1L,2L,and 3L express 1 layer,2 layers,and 3 layers,respectively.

    Apart from vacancies, interstitial atoms are also formed under the neutron irradiation condition. Figure 5 illustrates three different interstitial sites at the interface. The symbols,H,T,and B represent the hollow,top,and bridge position,respectively. The relative stabilities of the single interstitial C atom and Fe atom at the three sites are investigated. The interstitial Fe atom prefers to stay at the hollow site,and its formation energy is ~1.83 eV,which is lower than the formation energy for the tetrahedral site in bulk Fe.In addition,the interstitial atoms have a notable effect on the atomic configurations of the neighboring atoms. The interstitial Fe atom pushes the graphene layer up and affects the configuration of the Fe layers(see Fig.6(a)). The interstitial C atom prefers to stay in the Fe layer(Fig.6(b)),and its formation energy is 1.41 eV.These results suggest that the interstitial atoms can be easily trapped at the interface. Therefore, the interface is regarded as a sink that can trap intrinsic defects.

    Fig.5. Three candidate sites at Fe(110)–graphene interface (only part of atoms in an interface are displayed here for clarity), showing(a)side view and (b) top view of structure, where red, green, and blue balls represent hollow,bridge,and top sites,respectively.

    Fig.6. (a)Structure of interstitial Fe atom and(b)structure of the interstitial C atom at Fe(110)–graphene interface,with purple and gray balls representing Fe and C atoms,respectively.

    3.3. Stability and diffusion of He atoms at interface

    Under long-term neutron irradiation, a certain number of He atoms can be produced by the (n, α) transmutation reaction.[58–60]Then,He bubbles can form at the interface and grain boundaries,thereby resulting in the He embrittlement of the structural material.[56,61,62]Therefore,it is critical to investigate the effects of He atoms at the interface. After optimization, it is found that the interstitial He atoms at the T and B sites are unstable and spontaneously move to the H site. Thus,an interstitial He atom prefers to stay stably at the H site and the bottom of the C2site, the formation energy values for an interstitial He atom at these sites are 2.09 eV and 3.07 eV,respectively. Considering the energetics, the H site is the most stable, whereas the bottom of C2site is a metastable for He atoms. According to Fig.3, the H site and bottom of C2site have low electron density, and previous studies have shown that He atoms tend to be stable in areas with a low electron density.[62–64]

    Fig.7. Diffusion barrier profile of intersitital He atom at Fe(110)–graphene interface, indicating that He atom migrates from stable hollow site to the nearest neighboring hollow site, and diffusion path passes through another stable site of C2 bottom.

    Further, the diffusion of He atoms at the interface is vital for the formation of He bubbles. Therefore, He migration in Fe(110)–graphene is studied by the CI-NEB method. The energy for He migration between the two nearest neighbor H sites is calculated, and the result is presented in Fig.7. The value for this process is ~0.18 eV. In addition, the binding energy of two He atoms at the interface is ~1.36 eV.The interaction between He atoms is attractive,which is the driving force for its aggregation. As the migration barrier is small and the binding energy of He atoms is relatively large,the He atoms tend to aggregate at the interface.

    Graphene is impermeable to standard gases, including the He gas.[65]The He atom has a 1s closed shell electronic structure, and it does not interact chemically with graphene.Leenaerts et al.[66]preformed first principles calculations to investigate the penetration of He atoms through a graphene monolayer with a C vacancy.The diffusion barrier of graphene with a C vacancy is found to be ~18.8 eV with local density approximation (LDA) and 11.7 eV with GGA. Owing to the large migration energy, graphene can act as a barrier to impede the penetration of thermal equilibrium He at a temperature when the graphene layer remains stable. In this work,the penetration of He atoms is studied with a C vacancy in the Fe(110)–graphene system. First, a He atom is placed in vacuum far from the graphene surface to determine its stable site.After this optimization, the vertical distance between the He atom and interface is found to be ~2.896 ?A. Then, the migration of He atoms between the comfortable site and H site is investigated, and the result is presented in Fig.8. The migration energy is ~11.79 eV in this case. The high energy barrier restricts the diffusion of He across the graphene layer to reach the interface. The result illustrates that the impermeability of graphene is not reduced by the presence of Fe layers.Once some He atoms penetrate the graphene structure to reach the interface,they are trapped there and aggregated into larger species.

    Fig.8. Migration energy of He atom in Fe(110)–graphene system with a C vacancy: He atom migrates from vacuum to hollow site at interface though a C vacancy in graphene layer.

    At the same time,the He formation energy at the tetrahedral interstitial site in the Fe substrate is 5.00 eV, larger than that at the interface. This phenomenon strongly indicates that the Fe(110)–graphene interface acts as a sink that traps He atoms. In order to study the role of graphene, we calculate the diffusion barrier of a single He atom in a structure with seven Fe layers. The migration path is shown in Fig.9. The diffusion barrier is 7.24 eV,which is obviously lower than that for the Fe(110)–graphene system. Hence,it is concluded that the graphene acts as a buffer layer. Thus, the low formation energy and high diffusion barrier of He atoms at the interface delay the detrimental effects of He and allow the structural material to remain in service for longer.

    Fig.9. Diffusion barrier of a single He atom in structure with seven Fe layers,showing that barrier between vacuum and the first Fe layer is ~7.24 eV.

    4. Conclusions

    The behaviors of point defects and He atoms are investigated via ab initio calculations based on DFT, and the results are compared with those of bcc Fe (bulk) and a single graphene layer. The conclusions drawn from the present study are as follows.

    (i)A strong interaction and an intense Fe-3d–C-2p orbital hybridization are responsible for the stable graphene structure on the Fe(110)substrate.

    (ii) Vacancies and interstitial atoms are easily formed at the interface, and the interface can act as a sink for point defects.

    (iii)The He atoms require a large energy barrier to penetrate the graphene layer with a C vacancy and the binding energy of the He atoms is larger at the interface. This means that the interface impedes the diffusion of He atoms,and serves as a sink that traps the He atoms.

    Acknowledgement

    The authors are grateful to the Supercomputing Center of Dalian University of Technology and the Project of Nuclear Power Technology Innovation Center of Science Technology and Industry for National Defense for the computational support(Contract No.HDLCXZX-2019-ZH-28).

    性色av乱码一区二区三区2| 亚洲人成网站在线播放欧美日韩| 俺也久久电影网| 久久精品aⅴ一区二区三区四区| 精品久久久久久久人妻蜜臀av| 亚洲精品久久国产高清桃花| 免费电影在线观看免费观看| 国产男靠女视频免费网站| 亚洲在线观看片| 久久九九热精品免费| 美女高潮喷水抽搐中文字幕| 人人妻人人澡欧美一区二区| 中文在线观看免费www的网站| 色精品久久人妻99蜜桃| 国产精品自产拍在线观看55亚洲| 亚洲国产精品999在线| 91字幕亚洲| 欧美日韩国产亚洲二区| 国产成人av教育| 听说在线观看完整版免费高清| 亚洲av免费在线观看| 国产高潮美女av| 精品久久久久久成人av| 欧美成人性av电影在线观看| 亚洲片人在线观看| 日韩免费av在线播放| 婷婷精品国产亚洲av| 最近最新中文字幕大全电影3| 一边摸一边抽搐一进一小说| 亚洲国产精品999在线| 日本成人三级电影网站| 人妻丰满熟妇av一区二区三区| bbb黄色大片| 国产精品自产拍在线观看55亚洲| 一a级毛片在线观看| 国产激情久久老熟女| 亚洲aⅴ乱码一区二区在线播放| 999久久久国产精品视频| 日本在线视频免费播放| 久久久久久久午夜电影| 日本五十路高清| 757午夜福利合集在线观看| а√天堂www在线а√下载| 成人三级黄色视频| www.自偷自拍.com| 婷婷亚洲欧美| 久久天躁狠狠躁夜夜2o2o| 法律面前人人平等表现在哪些方面| 国产一级毛片七仙女欲春2| 国产1区2区3区精品| 国产欧美日韩一区二区精品| 一二三四社区在线视频社区8| 久久香蕉精品热| 国产成人av激情在线播放| 久久久久性生活片| 日韩高清综合在线| 精品久久久久久久毛片微露脸| 国产三级中文精品| 熟妇人妻久久中文字幕3abv| 日本在线视频免费播放| tocl精华| 噜噜噜噜噜久久久久久91| 国产又色又爽无遮挡免费看| 亚洲电影在线观看av| 精品国产乱码久久久久久男人| 欧美成人一区二区免费高清观看 | 丰满人妻一区二区三区视频av | 国内精品久久久久久久电影| 老鸭窝网址在线观看| 99国产综合亚洲精品| 国产一区二区在线av高清观看| 亚洲18禁久久av| 999久久久国产精品视频| 熟女电影av网| 天堂av国产一区二区熟女人妻| 成人18禁在线播放| 欧美黄色淫秽网站| tocl精华| 男女之事视频高清在线观看| 久久久久性生活片| 性色avwww在线观看| 亚洲精华国产精华精| 91av网站免费观看| 国产成人福利小说| 日韩欧美国产一区二区入口| 国产精品一区二区三区四区免费观看 | 国产精品一区二区免费欧美| 亚洲人成伊人成综合网2020| 天天躁日日操中文字幕| 老汉色av国产亚洲站长工具| 亚洲激情在线av| 精品人妻1区二区| 国产伦在线观看视频一区| av黄色大香蕉| 特大巨黑吊av在线直播| 国产精品亚洲av一区麻豆| 亚洲欧美激情综合另类| 亚洲欧美激情综合另类| 美女扒开内裤让男人捅视频| 观看免费一级毛片| 51午夜福利影视在线观看| 精品一区二区三区视频在线观看免费| 性欧美人与动物交配| 97超视频在线观看视频| 亚洲国产高清在线一区二区三| 午夜激情欧美在线| 日韩欧美精品v在线| 成人18禁在线播放| 美女高潮喷水抽搐中文字幕| 婷婷亚洲欧美| 精品久久久久久久久久免费视频| 亚洲人成电影免费在线| 嫩草影院入口| 两个人视频免费观看高清| 叶爱在线成人免费视频播放| 国产成人福利小说| 欧美黑人欧美精品刺激| 女生性感内裤真人,穿戴方法视频| 国产伦精品一区二区三区视频9 | 成人亚洲精品av一区二区| 免费看日本二区| 老司机福利观看| 久久热在线av| 成年女人毛片免费观看观看9| 欧美zozozo另类| 国产一区二区激情短视频| 亚洲国产欧洲综合997久久,| 国产一区二区在线观看日韩 | 可以在线观看的亚洲视频| 我要搜黄色片| 成在线人永久免费视频| 深夜精品福利| 男女午夜视频在线观看| 动漫黄色视频在线观看| 欧美乱色亚洲激情| 99久久精品一区二区三区| 天堂网av新在线| 国产综合懂色| 精品久久久久久久久久久久久| 国产精品久久电影中文字幕| 成人亚洲精品av一区二区| 成熟少妇高潮喷水视频| 禁无遮挡网站| 亚洲欧美一区二区三区黑人| 51午夜福利影视在线观看| 国产精品久久久久久人妻精品电影| 老鸭窝网址在线观看| 后天国语完整版免费观看| 国产69精品久久久久777片 | 两个人看的免费小视频| 久久草成人影院| 日韩欧美在线二视频| 国产在线精品亚洲第一网站| 人妻久久中文字幕网| 精品无人区乱码1区二区| 麻豆成人午夜福利视频| 男女视频在线观看网站免费| 看免费av毛片| 国产97色在线日韩免费| 夜夜夜夜夜久久久久| 久久久久性生活片| 亚洲一区高清亚洲精品| 欧美丝袜亚洲另类 | 国产黄a三级三级三级人| 美女高潮喷水抽搐中文字幕| 床上黄色一级片| 久久亚洲真实| 国产淫片久久久久久久久 | 看片在线看免费视频| 两人在一起打扑克的视频| 国产精品美女特级片免费视频播放器 | 成年人黄色毛片网站| av女优亚洲男人天堂 | 中文亚洲av片在线观看爽| 欧美日韩国产亚洲二区| 99国产精品99久久久久| 国产免费男女视频| 国产伦一二天堂av在线观看| 天天一区二区日本电影三级| 亚洲中文字幕日韩| 亚洲美女黄片视频| 日韩欧美一区二区三区在线观看| 国内揄拍国产精品人妻在线| 99re在线观看精品视频| 一级a爱片免费观看的视频| 亚洲欧美日韩无卡精品| 一a级毛片在线观看| 久久这里只有精品中国| 久久婷婷人人爽人人干人人爱| 色综合亚洲欧美另类图片| 岛国视频午夜一区免费看| 欧美丝袜亚洲另类 | 亚洲美女黄片视频| 男女午夜视频在线观看| 少妇人妻一区二区三区视频| 搡老岳熟女国产| 99re在线观看精品视频| 国产伦精品一区二区三区视频9 | 99精品在免费线老司机午夜| 精品久久久久久久久久免费视频| 精品国内亚洲2022精品成人| 国产精品99久久久久久久久| 国产一级毛片七仙女欲春2| 波多野结衣高清无吗| 免费电影在线观看免费观看| 偷拍熟女少妇极品色| 欧美乱妇无乱码| 亚洲第一欧美日韩一区二区三区| 三级毛片av免费| 午夜免费激情av| 国产69精品久久久久777片 | 日韩欧美国产一区二区入口| 他把我摸到了高潮在线观看| 午夜免费观看网址| 久久久水蜜桃国产精品网| 我要搜黄色片| 亚洲七黄色美女视频| 国产精品久久视频播放| 亚洲色图 男人天堂 中文字幕| 亚洲成a人片在线一区二区| 三级毛片av免费| 美女高潮的动态| 亚洲av电影不卡..在线观看| 制服人妻中文乱码| 淫妇啪啪啪对白视频| 又黄又粗又硬又大视频| 两性午夜刺激爽爽歪歪视频在线观看| 亚洲欧美精品综合一区二区三区| 午夜福利在线在线| 日韩欧美三级三区| 亚洲欧美一区二区三区黑人| av女优亚洲男人天堂 | 国产乱人视频| 1000部很黄的大片| 国产精品99久久99久久久不卡| 国产男靠女视频免费网站| 香蕉av资源在线| 搡老妇女老女人老熟妇| 午夜福利免费观看在线| 最近最新免费中文字幕在线| 久久精品国产99精品国产亚洲性色| 精品久久久久久成人av| 国产精品野战在线观看| 欧美日韩精品网址| 午夜福利18| 成人特级av手机在线观看| 最近最新免费中文字幕在线| 这个男人来自地球电影免费观看| 在线观看免费午夜福利视频| 久久久久性生活片| 久久草成人影院| 高清在线国产一区| 日日摸夜夜添夜夜添小说| 一个人看视频在线观看www免费 | 韩国av一区二区三区四区| 成年版毛片免费区| 两个人的视频大全免费| 亚洲自拍偷在线| 欧美黑人欧美精品刺激| 一二三四社区在线视频社区8| 亚洲18禁久久av| 亚洲av第一区精品v没综合| 日韩有码中文字幕| 欧美国产日韩亚洲一区| 国产精品亚洲美女久久久| 午夜福利高清视频| 久久精品影院6| 男女之事视频高清在线观看| 久久久久九九精品影院| 99在线视频只有这里精品首页| 在线观看免费午夜福利视频| 国产v大片淫在线免费观看| 怎么达到女性高潮| 精品不卡国产一区二区三区| 男人舔女人下体高潮全视频| 亚洲熟妇熟女久久| 听说在线观看完整版免费高清| 老鸭窝网址在线观看| 亚洲成a人片在线一区二区| 精品久久久久久久久久久久久| 中文字幕av在线有码专区| 精品国产亚洲在线| 亚洲乱码一区二区免费版| 久久香蕉国产精品| 精品国产乱码久久久久久男人| 一本久久中文字幕| 女人被狂操c到高潮| 国产精品一区二区免费欧美| 又黄又粗又硬又大视频| 动漫黄色视频在线观看| 美女大奶头视频| 国产av不卡久久| 亚洲精品美女久久av网站| 欧美激情在线99| 蜜桃久久精品国产亚洲av| 久久精品亚洲精品国产色婷小说| 看免费av毛片| 国产激情欧美一区二区| 亚洲 欧美一区二区三区| 国产毛片a区久久久久| 男人舔女人的私密视频| 国产免费av片在线观看野外av| 欧美日韩中文字幕国产精品一区二区三区| 亚洲aⅴ乱码一区二区在线播放| 欧美日韩一级在线毛片| 亚洲天堂国产精品一区在线| 亚洲av成人一区二区三| 两性午夜刺激爽爽歪歪视频在线观看| 人妻夜夜爽99麻豆av| 欧美av亚洲av综合av国产av| 精品久久久久久久毛片微露脸| 亚洲人与动物交配视频| 精品国内亚洲2022精品成人| 亚洲 欧美 日韩 在线 免费| 亚洲激情在线av| 舔av片在线| 黄片大片在线免费观看| 老司机福利观看| 中文资源天堂在线| 波多野结衣高清无吗| 国产精品自产拍在线观看55亚洲| 久久久久久久精品吃奶| 久久这里只有精品19| 成人一区二区视频在线观看| 亚洲国产精品合色在线| 97碰自拍视频| 国产黄a三级三级三级人| 1024手机看黄色片| 午夜久久久久精精品| 在线观看66精品国产| 悠悠久久av| 久久精品国产亚洲av香蕉五月| 琪琪午夜伦伦电影理论片6080| 久久精品91无色码中文字幕| 狂野欧美激情性xxxx| 天堂av国产一区二区熟女人妻| 国产亚洲精品久久久久久毛片| 搡老岳熟女国产| or卡值多少钱| 国产欧美日韩一区二区精品| 伦理电影免费视频| 少妇熟女aⅴ在线视频| 午夜福利高清视频| 亚洲av美国av| 亚洲国产欧美一区二区综合| 首页视频小说图片口味搜索| 一级毛片精品| 国产一级毛片七仙女欲春2| 大型黄色视频在线免费观看| 99在线人妻在线中文字幕| 国产精华一区二区三区| 免费观看精品视频网站| 国产爱豆传媒在线观看| 午夜福利免费观看在线| 免费在线观看亚洲国产| 日韩国内少妇激情av| 精品国产三级普通话版| 日本a在线网址| 真人一进一出gif抽搐免费| 欧美中文综合在线视频| 搞女人的毛片| 国产三级在线视频| 免费观看人在逋| 亚洲欧美精品综合久久99| 一级毛片精品| 欧美+亚洲+日韩+国产| 一个人免费在线观看的高清视频| 精品欧美国产一区二区三| 欧美最黄视频在线播放免费| 久久精品人妻少妇| av在线天堂中文字幕| 久久久久国产一级毛片高清牌| 成年版毛片免费区| 色噜噜av男人的天堂激情| а√天堂www在线а√下载| 亚洲一区高清亚洲精品| 欧美乱码精品一区二区三区| 伊人久久大香线蕉亚洲五| 亚洲av成人av| 精品欧美国产一区二区三| 九色国产91popny在线| 久久香蕉精品热| 亚洲激情在线av| 一本久久中文字幕| xxx96com| 亚洲 欧美 日韩 在线 免费| 久久中文看片网| 一本久久中文字幕| 观看免费一级毛片| 亚洲 欧美 日韩 在线 免费| 国产精品日韩av在线免费观看| 久久久国产成人精品二区| 国产精品乱码一区二三区的特点| 女人高潮潮喷娇喘18禁视频| 精品久久久久久久毛片微露脸| 很黄的视频免费| 99久久99久久久精品蜜桃| 亚洲真实伦在线观看| 极品教师在线免费播放| 精品日产1卡2卡| 又黄又粗又硬又大视频| 亚洲成人精品中文字幕电影| av视频在线观看入口| 亚洲在线自拍视频| 人人妻人人澡欧美一区二区| 日本 欧美在线| 国产精品电影一区二区三区| 亚洲国产精品999在线| 十八禁人妻一区二区| 波多野结衣巨乳人妻| 在线观看一区二区三区| 国产亚洲av嫩草精品影院| 少妇的逼水好多| 12—13女人毛片做爰片一| 日本五十路高清| 我要搜黄色片| 别揉我奶头~嗯~啊~动态视频| 国产人伦9x9x在线观看| 三级国产精品欧美在线观看 | 久99久视频精品免费| 成人精品一区二区免费| 久久久国产欧美日韩av| 嫩草影院入口| 脱女人内裤的视频| 国产精品久久久av美女十八| 性色avwww在线观看| 久久久久久久久中文| 国产一区在线观看成人免费| 亚洲精品久久国产高清桃花| 小蜜桃在线观看免费完整版高清| 午夜福利18| 色播亚洲综合网| 最新美女视频免费是黄的| 日韩欧美 国产精品| 嫩草影院精品99| 人妻久久中文字幕网| 变态另类成人亚洲欧美熟女| 欧美黑人欧美精品刺激| 在线观看免费午夜福利视频| 亚洲国产日韩欧美精品在线观看 | 国产乱人视频| 搡老妇女老女人老熟妇| 国产精品永久免费网站| 成年女人看的毛片在线观看| 久久久精品欧美日韩精品| 高清在线国产一区| ponron亚洲| 男女视频在线观看网站免费| 999精品在线视频| 久久精品夜夜夜夜夜久久蜜豆| 毛片女人毛片| 亚洲无线观看免费| 久久中文看片网| 日本黄色片子视频| 熟女电影av网| 琪琪午夜伦伦电影理论片6080| 国产精品亚洲av一区麻豆| 又黄又爽又免费观看的视频| 精品国产美女av久久久久小说| 麻豆国产av国片精品| 天天一区二区日本电影三级| 色吧在线观看| 狂野欧美白嫩少妇大欣赏| 亚洲自偷自拍图片 自拍| 97超视频在线观看视频| 国内精品久久久久久久电影| 亚洲 欧美 日韩 在线 免费| 日本a在线网址| 在线国产一区二区在线| 91麻豆精品激情在线观看国产| 国产美女午夜福利| 女同久久另类99精品国产91| 国产三级黄色录像| 久久人妻av系列| 午夜福利在线在线| 91久久精品国产一区二区成人 | 又大又爽又粗| 国产亚洲精品一区二区www| www.999成人在线观看| 成人三级做爰电影| 午夜福利高清视频| 国产成人精品久久二区二区91| 两个人看的免费小视频| 人人妻,人人澡人人爽秒播| 久久性视频一级片| 国产免费男女视频| 一二三四社区在线视频社区8| 色综合欧美亚洲国产小说| 国产极品精品免费视频能看的| 免费看美女性在线毛片视频| 国产 一区 欧美 日韩| 国产野战对白在线观看| 桃红色精品国产亚洲av| 国产成人精品久久二区二区免费| 国产主播在线观看一区二区| 欧美日韩一级在线毛片| 国产精品国产高清国产av| 亚洲精品美女久久久久99蜜臀| 性欧美人与动物交配| 午夜福利在线观看免费完整高清在 | 岛国在线观看网站| 免费高清视频大片| 老司机福利观看| 午夜福利高清视频| 嫩草影院入口| 色综合婷婷激情| 国产欧美日韩一区二区三| 国产单亲对白刺激| 日韩免费av在线播放| 这个男人来自地球电影免费观看| 欧美日本视频| 男女床上黄色一级片免费看| 99热这里只有精品一区 | 欧美黑人欧美精品刺激| 美女扒开内裤让男人捅视频| 国产野战对白在线观看| 国产麻豆成人av免费视频| 白带黄色成豆腐渣| 久久中文字幕一级| 免费一级毛片在线播放高清视频| 国产精品久久久久久精品电影| 亚洲第一欧美日韩一区二区三区| 97碰自拍视频| 两性夫妻黄色片| 亚洲精品一卡2卡三卡4卡5卡| 日本免费a在线| 窝窝影院91人妻| 国产精品久久久久久精品电影| 两人在一起打扑克的视频| 亚洲人成网站在线播放欧美日韩| 两个人视频免费观看高清| 亚洲中文日韩欧美视频| 美女高潮喷水抽搐中文字幕| 亚洲男人的天堂狠狠| 欧美+亚洲+日韩+国产| 亚洲成av人片免费观看| 婷婷精品国产亚洲av| 午夜亚洲福利在线播放| 精品久久久久久久人妻蜜臀av| 老汉色av国产亚洲站长工具| 午夜成年电影在线免费观看| 国产三级在线视频| 精品熟女少妇八av免费久了| 在线观看免费视频日本深夜| 男女之事视频高清在线观看| 成人精品一区二区免费| 十八禁网站免费在线| 国产激情久久老熟女| 免费看a级黄色片| 99久久国产精品久久久| 三级国产精品欧美在线观看 | 欧美日韩国产亚洲二区| 国产精品日韩av在线免费观看| 国产午夜福利久久久久久| 老鸭窝网址在线观看| 日本熟妇午夜| 免费观看人在逋| 香蕉久久夜色| 麻豆国产97在线/欧美| 久久久精品大字幕| 美女黄网站色视频| 成人18禁在线播放| 在线视频色国产色| av片东京热男人的天堂| 一区二区三区高清视频在线| 毛片女人毛片| 国产精品99久久久久久久久| 成年女人永久免费观看视频| 夜夜躁狠狠躁天天躁| 亚洲18禁久久av| 国产aⅴ精品一区二区三区波| 日本 av在线| 欧美另类亚洲清纯唯美| 亚洲国产看品久久| 午夜福利成人在线免费观看| 日韩成人在线观看一区二区三区| 99热6这里只有精品| 18禁观看日本| 可以在线观看的亚洲视频| 国产高潮美女av| 麻豆国产av国片精品| 亚洲一区二区三区色噜噜| 亚洲五月婷婷丁香| 精品国产亚洲在线| 男人的好看免费观看在线视频| 变态另类成人亚洲欧美熟女| 欧美激情在线99| 亚洲最大成人中文| 一夜夜www| 亚洲专区字幕在线| 偷拍熟女少妇极品色| 日韩欧美在线乱码| 久久久久久国产a免费观看| 中文字幕久久专区| 99精品欧美一区二区三区四区| 制服人妻中文乱码| 国产蜜桃级精品一区二区三区| 成人三级做爰电影| 巨乳人妻的诱惑在线观看| 99久久精品国产亚洲精品| 午夜免费成人在线视频| 非洲黑人性xxxx精品又粗又长| 999久久久国产精品视频| 国产淫片久久久久久久久 | 亚洲成人中文字幕在线播放| 欧美丝袜亚洲另类 | 动漫黄色视频在线观看| 黄片大片在线免费观看| 亚洲国产高清在线一区二区三| 一本久久中文字幕| 亚洲 欧美 日韩 在线 免费| 禁无遮挡网站| 国产极品精品免费视频能看的| 免费观看的影片在线观看| 动漫黄色视频在线观看|