本文選題：負(fù)熱膨脹　切入點(diǎn)：框架結(jié)構(gòu)　出處：《北京科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：框架結(jié)構(gòu)負(fù)熱膨脹(NTE)材料是一個(gè)比較龐大的NTE材料家族,其包括ScF_3、A_2M_3O_(12)(A=三價(jià)金屬離子,M=W或Mo)、ZrM_2O_8(M=W或Mo)、MOF等,其相結(jié)構(gòu)和熱膨脹的研究具有重要的學(xué)術(shù)意義和潛在的應(yīng)用價(jià)值。本文主要選擇A_2W_3O_(12)和ZrM_2O_8為研究對象,雖然人們對這兩類材料已經(jīng)進(jìn)行了大量的研究,但皆是圍繞陽離子的替代去調(diào)控相變溫度和熱膨脹性。本文通過在框架結(jié)構(gòu)中引進(jìn)客體小分子和采用高溫淬火手段對其進(jìn)行改性,進(jìn)而研究其結(jié)構(gòu)、相轉(zhuǎn)變和熱膨脹性的改變。主要內(nèi)容如下：氨化使小分子(NH_3)進(jìn)入了ZrW_2O_8晶格內(nèi),與W_2形成弱配位鍵,并與近鄰原子發(fā)生相互作用,進(jìn)而改變了相變溫度和負(fù)熱膨脹性。氨化使ZrW_2O_8的相變溫度提高了近50℃,使其負(fù)熱膨脹系數(shù)由-7.8×10~(-6)℃~(-1)調(diào)節(jié)到了-2.1×10~(-6)℃~(-1)。產(chǎn)生這些改變的原因主要包括兩方面：一方面,NH_3的進(jìn)入填充了晶格間隙,減小了材料收縮的空間,使ZrW_2O_8的整體框架結(jié)構(gòu)剛性增強(qiáng)；另一方面,NH_3與近鄰原子相互作用,束縛了氧原子的橫向熱振動(dòng)。氨化還可以防止ZrW_2O_3水化,提高其穩(wěn)定性。另外,對ZrMo_2O_8,ZrWMoO_8和Y_2W_3O_(12)也都進(jìn)行了氨化。ZrMo_2O_8和ZrWMoO_8氨化后,其變化趨勢和ZrW_2O_8類似。Y_2W_3O_(12)經(jīng)過氨化后,晶體結(jié)構(gòu)發(fā)生了改變。室溫下,Dy_2W_3O_(12)呈單斜相,不具有負(fù)熱膨脹性；升高到一定溫度時(shí),轉(zhuǎn)變?yōu)榫哂胸?fù)熱膨脹性的正交相,相變溫度為996℃。通過高溫淬火的方式,Dy_2W_3O_(12)的高溫正交相被保留至低溫。正交相Dy_2W_3O_(12)在500℃以下可以穩(wěn)定存在,其負(fù)熱膨脹系數(shù)為αv=-2.6×10~(-5)℃~(-1)。到目前為止,Dy_2W_3O_(12)是A_2W_3O_(12)系列負(fù)熱膨脹材料中負(fù)熱膨脹系數(shù)最大的。另外,對其發(fā)光和磁性也進(jìn)行了研究。Ho_2W_3O_(12)低溫時(shí)的相結(jié)構(gòu)一直是個(gè)有爭議的問題。本文通過不同的制備條件(包括高溫淬火)成功地解決了這個(gè)爭議。研究發(fā)現(xiàn)：低溫時(shí),Ho_2W_3O_(12)的熱力學(xué)穩(wěn)定相為單斜相,高溫時(shí)為正交相。由于正交相向單斜相的轉(zhuǎn)變是一個(gè)緩慢的過程,故低溫時(shí)的相組成與制備時(shí)的降溫速率緊密相關(guān)。當(dāng)降溫速率為10℃/min時(shí),Ho_2W_3O_(12)就可以完全使高溫時(shí)的正交相保留至低溫。正交相Ho_2W_3O_(12)在600℃下可穩(wěn)定存在,負(fù)熱膨脹系數(shù)為-2.1×10~(-5)℃~(-1)。在Gd_xTm_(2-x)W_3O_(12)(x=0.5、1和1.5)固溶體中,Gd含量較低(x=0.5)時(shí),室溫穩(wěn)定相為正交相；Gd的含量較高(x=1,1.5)時(shí),室溫穩(wěn)定相變?yōu)閱涡毕?并在高溫時(shí)轉(zhuǎn)變?yōu)檎幌�。采用高溫淬火的方�?Gd_xTm_(2-x)W_3O_(12)(x=1,1.5)的高溫正交相被保留至室溫,并且在500℃以下穩(wěn)定存在。Gd_(0.5)Tm_(1.5)W_3O_(12)的吸水性較弱,而正交相Gd_xTm_(2-x)W_3O_(12)(x=1.1.5)吸水性則較強(qiáng)。Gd_xTm_(2-x)W_3O_(12)在200～5000C的溫度區(qū)間內(nèi)均具有較大的負(fù)熱膨脹性,并且其負(fù)熱脹系數(shù)隨著Gd的含量增加而增大。引進(jìn)客體小分子和采用高溫淬火拓展了A_2W_3O_(12)、ZrM_2O_8等框架結(jié)構(gòu)類負(fù)熱膨脹材料的研究途徑,無論在理論研究上,還是在實(shí)際應(yīng)用中,都有著重要意義。
[Abstract]:Frame structure of negative thermal expansion (NTE) material is a relatively large NTE family of materials, including ScF_3, A_2M_3O_ (12) (A= M=W trivalent metal ions, or Mo), ZrM_2O_8 (M=W or Mo), MOF, to study the phase structure and thermal expansion has important application value and academic significance potential. This paper chooses A_2W_3O_ and ZrM_2O_8 (12) as the research object, although there have been a lot of studies on the two kinds of materials, but are instead around the cation to control the phase transition temperature and thermal expansion. In this paper, through the introduction of small molecule object and it was modified by high temperature quenching method in the frame structure, and then study the structure, the change of phase transformation and thermal expansion. The main contents are as follows: ammonization of the small molecule (NH_3) into the ZrW_2O_8 lattice, forming a weak coordination bond with W_2, and interact with the neighboring atoms, thereby changing the phase transition temperature And the negative thermal expansion. The ammoniation transformation temperature of ZrW_2O_8 increased by nearly 50 degrees, the negative thermal expansion coefficient by -7.8 * 10~ (-6) C ~ (-1) adjusted to -2.1 * 10~ (-6) C ~ (-1). The causes of these changes mainly includes two aspects: on the one hand, enter the lattice filled the gap of NH_3, reduce the shrinkage of space, so that the overall rigid frame structure of ZrW_2O_8 was enhanced; on the other hand, NH_3 and nearest neighbor atoms bound the transverse thermal vibration of oxygen. Ammonification can also prevent ZrW_2O_3 hydration, improve its stability. In addition, the ZrMo_2O_8, ZrWMoO_8 and Y_2W_3O_ (12) were.ZrMo_2O_8 and ZrWMoO_8 after ammoniation ammonification, the trend is similar to ZrW_2O_8.Y_2W_3O_ (12) after ammoniation changed after the crystal structure at room temperature, Dy_2W_3O_ (12) in the monoclinic phase, with negative thermal expansion; increased to a certain temperature, change into Negative thermal expansion of the orthorhombic phase, phase transition temperature of 996 DEG. Through high temperature quenching method, Dy_2W_3O_ (12) orthogonal phase was retained to high temperature low temperature. The orthogonal phase Dy_2W_3O_ (12) at 500 DEG C can exist stably, the negative thermal expansion coefficient alpha v=-2.6 * 10~ (-5) C ~ (-1). So far, Dy_2W_3O_ (12) A_2W_3O_ (12) series of negative thermal expansion materials in negative thermal expansion coefficient of the maximum. In addition, the luminescent and magnetic properties were also studied in.Ho_2W_3O_ (12) phase structure at low temperature has been a controversial issue. This article through different preparation conditions (including high temperature quenching) successfully solved the dispute. It is found that at low temperature, Ho_2W_3O_ (12) phase is thermodynamically stable monoclinic phase, high temperature to orthorhombic phase. Due to the change of orthorhombic to monoclinic phase is a slow process, so the temperature when the phase composition is closely related with the preparation of the cooling rate. 褰撻檷娓╅，

本文編號(hào)：1564132