Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Other materials

The Synthesis and Thermal Expansion Property of Yb2-xAlxMo3O12

Author LiQiuJie
Tutor YuanBin;LiangErJun
School Zhengzhou University
Course Optical Engineering
Keywords Negative Thermal Expansion A2Mo3O12 Yb2-xAlx MoO4 3 Absorbent Phase change
Type Master's thesis
Year 2011
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In recent years, due to the improvement of the performance requirements of the expansion of the materials, the negative thermal expansion (Negative thermal expansion, referred to as NTE) material to receive widespread attention. Wherein the general formula for tungsten of A2M3012 (Mo) salts negative thermal expansion material because of its larger anisotropic negative thermal expansion coefficient, but also within a wide temperature range are shown a negative thermal expansion characteristics, so that in the optical, electronic, medical, equipment and many other areas have a great potential value. The compounds A2M3012 quadrature phase, monoclinic, tetragonal phase three crystal structure. Generally only the orthogonal structure A2M3012 material that has a negative thermal expansion effects. Its crystal structure and A3, M6 related A2 (WO4) 3-series material, When A3 ionic radii are located the La3 Dy3 when monoclinic structure, A3 ionic radius of Ho3 to Al3 between when the quadrature phase structure. For A2 (MoO4) 3 materials When A3-ion radius between La3 ion radius of the the Gd3 ion radius between the crystalline material in the tetrahedral structure; A3-ion radius between Y3 to Lu3 when material crystallization quadrature phase structure. Reportedly, A2M3012 series of negative thermal expansion material, with the A3 radius becomes large, the negative coefficient of thermal expansion of the material is also greater. A3 ion radius greater than a certain degree, the structure of the material will become evacuated lattice water molecules easy material to affect the performance of the material of negative thermal expansion. For A2M3012 series of negative thermal expansion material is not enough sound, not many have been found A2M3012 series of negative thermal expansion material, and have been found A2M3012 series of negative thermal expansion materials exist some flaws, such as the phase transition temperature, room temperature under the water absorption and other issues, is not conducive to a wide range of application of the material. In order to look for the negative thermal expansion material, to further explore the mechanism of negative thermal expansion, to study the basic physical properties of negative thermal expansion coefficient controlled material, this paper, the use of high temperature rapid sintering method Yb2-xAlx (MoO4) 3 Series materials were synthesized, and the use of at room temperature X-ray powder diffraction pattern at room temperature and high temperature Raman spectroscopy, thermal analysis and analytical means such prepared samples were analyzed to study the thermal expansion, phase transition, the basic physical properties such as water-absorbent. The mechanism of the negative thermal expansion of A2M3012 series of negative thermal expansion material can be explained based on the bridging oxygen atoms in low-energy transverse thermal vibration of \The main contents are: synthesis the the Yb2 - xAlx (MoO4) 3 Series solid solution. Raman spectra showed that (1) YB2-xAlx (MoO4) 3 (x = 0-0.4) with pure Yb2Mo3O12 sample crystal structure, are quadrature phase structure, space group pncA. Samples YB2-xAlx (MoO4) 3 (x = 0-0.4) at room temperature with highly absorbent, as the temperature increases, the release of water molecules twice. Displayed on the temperature-dependent Raman spectra for the three-Yb2M3O12 characteristic Raman peak with increasing temperature, becoming more and more sharp and split. At room temperature, the material absorbs water molecules will hinder the phonon vibration mode inside the crystal, the material loss of negative thermal expansion properties. (2) YB2-xAlx (MoO4) 3 (x = 1.8-2.0) is a monoclinic structure with pure Al2Mo3O12 sample crystal structure at room temperature, does not show negative thermal expansion effect, but as the temperature rises, samples from a single monoclinic phase steering quadrature phase shift, showing the effect of negative thermal expansion. The study found that, by doping the Yb3 can effectively reduce the phase transition temperature of the Al2Mo3O12.

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