Preparation,Structure,Negative Thermal Expansion Property,Thermal Shrink Mechanism And Al Matrix Composites Of Zr_0.70V_1.33Mo_0.67O_6.73

Most materials have the property of "thermal expansion",when heated,thermal stress and microcracks will appear in the device,which is made of different materials,due to the mismatch of the coefficient of thermal expansion,this lead to a drop or even a failure in physical properties of the device.Fortunately,the negative thermal expansion materials can be compounded with ordinary positive thermal expansion materials and prepared thermal expansion materials which have controlled thermal expansion or zero thermal expansion to address the problems of the mismatch of the coefficient,and it will have a good potential value.However,there are still a lot of shortages in present negative thermal expansion materials,for instance,the raw materials are expensive,the preparation process is complicated,the negative thermal expansion temperature zone is narrow or not contains common temperature range.Therefore,it is necessary to find a kind of material which is easy to be prepared,has low cost and stable negative thermal expansion property in a wide temperature range.In this paper,we first synthesized a novel negative thermal expansion?NTE?material of Zr_0.70V_1.33Mo_0.67O_6.73 by solid state reaction method.It's structure,thermal expansion property and thermal shrink mechanism were studied.The main research work and results are as follows:?1?We synthesized Zr_0.70V_1.33Mo_0.67O_6.73 by solid state reaction method.It exhibits a stable negative thermal expansion property at least from 103 K to 773 K.It's average linear coefficients of thermal expansion?CTEs?were calculated to be-3.75 × 10-6 K-1?163 – 673 K?and-4.08 × 10-6 K-1?RT – 773 K?,and the intrinsic linear CTEs were calculated to be-3.84 × 10-6 K-1?103-473 K?and-4.22 × 10-6 K-1?RT-673 K?;?2?Zr_0.70V_1.33Mo_0.67O_6.73 crystals belong to the cubic system,space group Pa-3?No.205?with (6 = 8.93063 ?,V = 712.27316 ?3.And the crystals are composed of quasi-rigid VO4 or MoO4 tetrahedra and Zr O6 octahedra by linkages of corner shared,and its thermal shrink mechanism can be explained by quasi-rigid unit modes?QRUMs?.As the temperature increases,the vibration of polyhedra increases,the tilts and rotations of MoO4 and VO4 tetrahedra,will necessarily drag the Zr O6 octahedra along with it,and pull the rest of the structure in,giving a volume reduction,then present a NTE property in macro.And the phase transition temperature of Zr_0.70V_1.33Mo_0.67O_6.73 has been reduced,this may be attributed to the incorporation of cubic ZrMo2O8 structure and partially occupied Zr atoms?4a?.The tilts and rotations of polyhedra are easier with the increase of vacancy,and then lead the sample exhibits NTE in lower temperature.?3?We synthesized Al/Zr_0.70V_1.33Mo_0.67O_6.73 cermet composites by solid state reaction method.The composites are composed of Al and Zr_0.70V_1.33Mo_0.67O_6.73 excluding other impurity phase.The CTEs and impedance of the composite can be continuous regulated by adjust the Al content.The composites exhibit the capacitance and resistance characteristics as the content of Al is lower and bigger,respectively.In particularly,when Al : Zr_0.70V_1.33Mo_0.67O_6.73 = 4:6,the cermet composite not only has great conductivity,but also its average linear CTE is less than half of Al.The Al/Zr_0.70V_1.33Mo_0.67O_6.73 cermet composites will have good application prospection.