【作者】 傅力；

【导师】 王传彬；

【作者基本信息】 武汉理工大学 ， 材料学， 2010， 硕士

【摘要】 稀土元素掺杂的Bi4Ti3O12铁电薄膜作为一种无铅环保、性能优良的功能材料,可望替代锆钛酸铅(PZT)和钽酸锶铋(SBT)等薄膜材料,在铁电随机存储器等功能器件中得以应用。论文以Ho掺杂Bi4Ti3O12(Bi3.6Ho0.4Ti3O12)薄膜的制备及其铁电性能为研究目标,以固相反应和热压烧结的Ho掺杂Bi4Ti3O12陶瓷为靶材,利用脉冲激光沉积技术制备Bi3.6Ho0.4Ti3O12薄膜,以期望为新一代存储器的应用提供一种环境友好、性能良好的铁电新材料。论文首先以Bi2O3、TiO2和Ho2O3微粉为原料,利用固相反应法合成出不同Ho掺杂量的Bi4-xHoxTi3O12粉体,然后采用热压烧结技术将其致密化,研究了合成和烧结工艺参数(合成温度、烧结温度、Bi过量)以及Ho掺杂量对Bi4-xHoxTi3O12粉体和陶瓷的结构及性能的影响,并确定了适宜的制备工艺：先在Bi2O3过量3wt%、合成温度900℃、保温时间8h条件下合成Bi4-xHoxTi3O12粉体；再将粉体在850℃-30MPa下热压烧结2h得到Bi4-xHoxTi3O12陶瓷。在上述条件下得到的Bi3.6Ho0.4Ti3O12陶瓷物相单一,结构致密(致密度99.4%),可作为高质量靶材,进一步制备Bi3.6Ho0.4Ti3O12铁电薄膜。介电和铁电性能测试表明,随着Ho掺杂量的增加,Bi4-xHoxTi3O12陶瓷的晶粒逐渐减小,致密度也略有下降,其介电常数和剩余极化强度均呈现先升高后降低的趋势,而介电损耗则先降低后升高。适宜的Ho掺杂量为0.4,在1MHz测试频率下,Bi3.6Ho0.4Ti3O12陶瓷的介电常数为207.3,介电损耗为0.0066,剩余极化强度为6.96μC/cm2。其次,以物相单一、整体致密的Bi3.6Ho0.4Ti3O12陶瓷为靶材,进一步利用脉冲激光沉积技术在Pt(111)/Ti/SiO2/Si衬底上制备Bi3.6Ho0.4Ti3O12铁电薄膜,重点研究了沉积工艺参数(激光能量密度、衬底温度、氧压)对薄膜物相、结晶取向、表面形貌和铁电性能的影响。结果表明,随着衬底温度的升高,薄膜的结晶性变好,600℃和700℃时,均能获得物相单一、结晶良好的Bi3.6Ho0.4Ti3O12薄膜,且薄膜分别呈c轴择优取向和随机取向；随着激光能量密度的提高,沉积薄膜逐渐由Bi2Ti2O7焦绿石相转变为Bi4Ti3O12类钙钛矿相,高于24.53J/cm2时,得到了物相单一的Bi3.6Ho0.4Ti3O12薄膜；提高氧压可获得单一物相的Bi3.6Ho0.4Ti3O12薄膜,且薄膜晶粒先增大后减小,而其结晶取向性无明显变化。适宜的脉冲激光沉积条件为29.3J/cm2-700℃-10Pa,在该条件下Bi3.6Ho0.4Ti3O12铁电薄膜物相单一,表面平整致密,而且具有较大的剩余极化强度(22.74μC/cm2)。更多还原

【Abstract】 As a ferroelectric functional material, rare earth elements doped bismuth titanate (Bi4Ti3O12) with large remanent polarization and low crystallization temperature is a possible substitute for lead zirconate titanate and bismuth-strontium tantalate in ferroelectric random access memory. The purpose of the present dissertation is to prepare a holmium doped bismuth titanate (Bi3.6Ho0.4Ti3O12) thin film and study its ferroelectric property, expecting to provide a environmentally-friendly ferroelectric material with good performance.As a ferroelectric functional material, rare earth elements doped bismuth titanate (Bi4Ti3O12) with large remanent polarization and low crystallization temperature is a possible substitute for lead zirconate titanate and bismuth-strontium tantalate in ferroelectric random access memory.Firstly, Ho3+doped Bi4Ti3O12 (Bi4-xHoxTi3O12) powders were fabricated by solid state reaction using Bi2O3, TiO2 and HO2O3 micro-powders as the raw materials. Then, Bi4-xHoxTi3O12 ceramic targets were obtained by densifying the synthesized powders using hot-pressed sintering. The influences of process parameters (synthesis temperature, sitering temperature, Bi content and Ho doping content) on the structure and property of the Bi4-xHoxTi3O12 powders and ceramic targets were studied, and the appropriate preparation conditions were achieved. That is, Bi4-xHoxTi3O12 powders were synthesized at 900℃for 8h with 3wt% excessive content of Bi2O3, and the powders were further sintered at 850℃-30MPa for 2h to prepare the Bi4-xHoxTi3O12 ceramics. The appropriate Ho content is 0.4, and Bi3.6Ho0.4Ti3O12 ceramic obtained under the appropriate preparation conditions showed pure phase and dense structure (about 99.4%), whose dielectric constant, dielectric loss and remanent polarization were 207.3,0.0066 and 6.96μC/cm2, respectively.Subsequently, we used the dense and pure phase Bi3.6Hoo.4Ti3O12 ceramic as the target to prepare Bi6Ho0.4Ti3O12 thin films on Pt(111)/Ti/SiO2/Si substrates by pulsed laser deposition. The effects of deposited parameters, such as substrate temperature, laser energy density and oxygen pressure, on the phase, orientation, surface morphology and ferroelectric property were mainly investigated. The results showed that the crystallinity of the as-deposited films increased with substrate temperature, and pure phase and well-crystallized Bi3.6Ho0.4Ti3O12 thin films were obtained at 600℃and 700℃with c-axis and random orientations, respectively. As the laser energy density increased, the phases of the films changed from Bi2Ti2O7 to Bi4Ti3O12, and pure Bi3.6Ho0.4Ti3O12 thin films were obtained at laser energy density higher than 24.53J/cm2. The pure Bi3.6Ho0.4Ti3O12 thin films could also be obtained by raising oxygen pressure. The grain sizes increased with oxygen pressure at first and then reduced, while the orientation changed little. The Bi3.6Ho0.4Ti3O12 thin film deposited under the appropriate conditions (29.3J/cm2-700℃-10Pa) exhibited a pure phase, smooth and dense surface, and the maximum remanent polarization was 22.74μC/cm2.更多还原