【作者】 蔡方硕；

【导师】 李来风；

【作者基本信息】 中国科学院研究生院（理化技术研究所） ， 凝聚态物理， 2009， 硕士

【摘要】 采用元素掺杂合成了以锰氮化合物为基的低温下具有负热膨胀性能的材料,并对影响负热膨胀性能的因素进行了研究。通过对材料的磁相转变与负热膨胀转变关系的研究,讨论了此类材料的负热膨胀机理。以Mn₃(Cu_0.6Ge_0.4)N材料为基础,分别掺杂了Nb、Cr、Re元素,对样品的物相和负热膨胀性能进行测试,发现Nb元素的掺杂可以使此类材料的负热膨胀温区向低温区移动,并且使得材料的负热膨胀温区得到拓宽,样品Mn₃(Cu_0.6 Nb0.15Ge0.25)N和Mn 3 (Cu_0.6Nb0.2Ge0.2)N的负热膨胀温区比未掺杂样品宽60%。样品Mn₃(Cu_0.6Nb0.15Ge0.25)N在165-210K温度范围内,其线膨胀系数达到-19.5×10^-6 K^-1;掺杂Cr元素取代Mn元素材料,随Cr含量的增加,样品负热膨胀产生的温区向低温区移动,样品Mn 2.55 Cr_0.45(Cu_0.6Ge_0.4)N在80-150K温度区间内,平均线膨胀系数为-19.14×10^-6 K^-1;用Re元素掺杂Mn₃(Cu_0.6Ge_0.4)N材料,发现可以通过Re元素的掺杂调节此类材料的热膨胀系数,样品Mn₃(Cu0.4Re0.2Ge_0.4)N在220K到315K的温区内都具有接近于零的热膨胀系数;对于“零膨胀”材料的研究表明,很多此类掺杂锰氮化合物材料在不同温区具有低膨胀或接近“零膨胀”的性质。对材料的磁性能研究发现:Mn₃(Cu_0.6 Nb xGe_0.4-x)N的负热膨胀转变与两类磁相变相关:一是在较高温度、较低掺杂浓度时,材料的负热膨胀转变温度与材料顺磁相和反铁磁相转变相关;二是在低温区、高掺杂浓度时,材料的负热膨胀转变与顺磁相和铁磁相转变相关,进一步研究表明,此种磁相转变是顺磁相和磁自旋玻璃态的转变,而磁自旋玻璃有可能是产生材料宽负热膨胀温区的物理本质;对材料Mn 3 (Cu_0.6-xRe x Ge_0.4)N的磁化率研究进一步证实了此类负热膨胀材料的负热转变与磁相转变的相关性。Mn₃(Cu_0.35 Re_0.25Ge_0.4)N材料的“零膨胀”现象可能是材料多元相热膨胀相互抵消的结果。更多还原

【Abstract】 The manganese nitride negative thermal expansion （NTE） materials were obtained by elements doping method, and their NTE properties at cryogenic temperatures were also investigated. The mechanism of NTE in these materials is discussed through the analysis on magnetic phase transition.Nb, Cr and Re were selected as doping elements in the Mn₃(Cu_0.6Ge_0.4)N matrix. By investigating their crystal structures and thermal expansion properties, we found that Nb doping can shift the NTE occurring-temperature window to low temperature region, and the NTE operation-temperature （ΔT） are also broadened, theΔT of Mn₃(Cu_0.6 Nb_0.15Ge_0.25)N and Mn₃ (Cu_0.6Nb_0.2Ge_0.2)N can reach 60% larger than Mn₃(Cu_0.6Ge_0.4)N. The coefficient of expansion （CTE） for Mn₃ (Cu_0.6Nb_0.15Ge_0.25)N is of -19.5×10^-6 K^-1 at 165-210K; TheΔT of Mn₃-xCrx(Cu_0.6Ge_0.4)N can shift to low temperature region with the increase of Cr content, Mn_2.55 Cr_0.45(Cu_0.6Ge_0.4)N has a CTE of -19.14×10^-6 K^-1 at 80-150K; The CTE changes with Re doping, Mn₃(Cu_0.35 Re_0.25Ge_0.4)N has a very low linear CTE at 220-315K。By measuring the magnetic property, we found that the NTE transitions of Mn₃(Cu_0.6 Nb x Ge_0.4-x)N are related with two types of magnetic phase transition: firstly, at high temperature region, with low doping concentration, the NTE transition is in a good coincidence to the paramagnetic phase and anti-ferromagnetic phase transition; Secondly, at low temperature region, with high doping concentration, the NTE transition is coincidence to the paramagnetic phase and ferromagnetic phase transition, further studies have shown that such magnetic phase transition may created a spin-glass system, which may be a reason for the broadening of the NTE operation-temperature window. The magnetic studies of low expansion materials show that the“zero-expansion”of Mn₃ (Cu_0.35 Re_0.25Ge_0.4)N may be a result of multi-phase effect.更多还原