【作者】 范协诚；

【导师】 陈湘明；

【作者基本信息】 浙江大学 ， 材料学， 2008， 博士

【摘要】 系统地研究了属于14/mmm空间群的MRAlO₄（M=Sr,Ca;R=La,Nd,Sm,Y）基微波介质陶瓷的制备、结构、微波介电性能及其随成分与结构变化的规律,并基于上述规律对CaSmAlO₄基陶瓷进行了改性,取得如下主要结论与成果:建立了一套包括开腔法和闭腔法的微波介电性能的测量评价系统。对复介电常数的数值计算的算法进行了改进,大幅度提高了计算效率,从而间接地提高了计算精度,并利用改进算法拓展了闭腔法的应用范围。通过XRD全谱拟合对MRAlO₄（M=Sr,Ca;R=La,Nd,Sm,Y）陶瓷的晶体结构进行精修。AlO₆八面体和（M,R）P₉十二面体在c轴方向分别受到强烈拉伸和强烈压缩,而在ab平面内的情况则正好相反。层间尺寸失配和层间极化是造成多面体畸变的两个主要原因,它们可以分别用结构许容因子和氧八面体畸变程度（或者（M,R）O₉中心阳离子与O（2a）原子面的距离）来衡量。随着结构许容因子的减小,（M,R）O。的畸变加剧,而AlO₆的畸变基本保持不变。根据键价理论的分析,SrYAlO₄的不稳定性和CaLaAlO₄的亚稳定性分别是由共同占据A位的两种阳离子的离子半径相差太大和离子价态相差太大造成的。为了从极性声子模的角度理解MRAlO₄（M=Sr,Ca;R=La,Nd,Sm,Y）陶瓷的微波介电响应的本质,测量了MRAlO₄陶瓷50～4000cm^-1范围内的红外反射光谱,利用K-K关系、经典谐振子模型对红外数据进行分析,并将红外数据外推到微波频段以估计本征微波介电损耗。（M,R）-AlO₆沿着ab平面的弯曲振动模和沿着c轴的伸缩振动模是对微波介电常数和介电损耗起主要贡献的两个模式。（M,R）O₉十二面体的畸变极大地影响了这两个模式的色散参数,从而决定了极化率和本证损耗,这就是MRAlO₄实测的极化率大幅度偏离氧化物加和法则得到的预测值以及MRAlO₄的Qf计算值随着结构许容因子的减小而减小的原因。减小本征介电损耗的关键是减小（M,R）O₉十二面体的畸变。Qf计算值大大高于实测值,表明通过优化微结构还能大幅度减小非本征损耗。通过改变CaO、Sm₂O₃和Al₂O₃的配比,研究了CaSmAlO₄基陶瓷的相组成及其对微结构和微波介电性能的影响。在（2+2x）CaO～（1-x）Sm₂O₃～Al₂O₃（x=-0.10,-0.05,0,0.05,0.10,0.20）陶瓷中,当x＞0时检测到Ca₃Al₂O₆和CaO第二相,而当x≤0时则是SmAlO₃和Sm₂O₃第二相。在（2+2x）CaO·Sm₂O₃·Al₂O₃（x=-0.02,-0.01,0,0.02,0.04）陶瓷中,当x＞0时检测到CaSmAl₃O₇、CaO和Sm₂O₃第二相,而当x≤0时,检测到SmAlO₃第二相。Ca₃Al₂O₆和SmAlO₃第二相会大幅度降低体系的Qf值,而CaSmAl₃O₇、CaO和Sm₂O₃第二相对体系的Qf值的不利影响很小甚至有利于Qf值的提高。在（2+2x）CaO·Sm₂O₃·Al₂O₃（x=0.02,0.03,0.04）陶瓷中获得了优异的微波介电性能:ε_r=19,Qf=120,000～125,300GHz,τ_f=-10～-9ppm/℃。通过Ca/Ti协同置换对CaSmAlO₄进行改性,得到了Ca_1+xSm_1-xAl_1-xTi_xO₄（0≤x≤0.4）陶瓷。对于Ca_1+xSm_1-xAl_1-xTi_xO₄主相而言,随着x的增大,晶胞参数a和c分别线性地增大和减小;（Al,Ti）O₆八面体的畸变略有减小,而（M,R）O₉十二面体的畸变逐渐加大,后者是晶胞参数c减小的原因。Ca_1+xSm_1-xAl_1-xTi_xO₄陶瓷具有良好的微波介电性能,尤其是当0.06≤x≤0.2时（ε_r≈20,Qf=96,500～118,700GHz,τ_f=-8～2ppm/℃）。当x=0时检测到了少量的SmAlO₃第二相,而当x≥0.15时检测到了微量的CaTiO₃第二相;在x=0和0.02成分点1500℃烧结的样品中观察到晶粒的异常长大。抑制这些微结构的产生有助于改善体系的微波介电性能。适当加入过量的CaO,Ca_1+xSm_1-xAl_1-xTi_xO₄基陶瓷的微波介电性能得到进一步改善,当x=0.15时,实现了极其优异的微波介电性能（ε_r=20.2,Qf=100,000GHz和τ_f=0.5 ppm/℃）。更多还原

【Abstract】 Synthesis,structures,and microwave dielectric properties of MRAlO₄-based（M=Ca, Sr;R=La,Nd,Sm,Y） ceramics with I4/mmm space group were systermatically investigated together with their property-structure relationship,and based on these findings,the modification of microwave dielectric properties was carried out for CaSmAlO₄ ceramics through structure tailoring and microstructure control.The following primary findings and/or achiements were obtained:An evaluation system involving the open cavity method and the closed cavity method was built up to characterize the microwave dielectric properties with high accurately.An innovative algorithm for numerical calculation of complex permittivity was developed,and the computational efficiency was improved greatly.With the algorithm,the application scope of the close cavity method was significantly extended.Crystal structure refinements were carried out for MRAlO₄ ceramics by Rietveld method.Along the c axis,AlO₆ octahedra and（M,R）O₉ dodecahedra were heavily stretched and compressed,respectively,while within the ab plane,the situation was reversed.The interlayer size mismatch and the interlayer electric polarization were the primary reasons for these distortions,and they could be evaluated with the tolerance factor and the deformation degree of octahedron（or the distance from（M,R） cation to O（2a） atomic plane）,respectively.As the tolerance factor decreased,the distortion of AlO₆ octahedra kept nearly unchanged,while that of（M,R）O₉ increased.Based on the analysis by the bond valence method,the instability of SrYAlO₄ and the metastability of CaLaAlO₄ were attributed to large differences of ionic radius and of apparent bond valence between M and R cations,respectively.To understand the dielectric nature of MRAlO₄ ceramics in terms of phonon modes,Fourier transform infrared reflectivity spectra in the range of 50-4000 cm^-1 were measured and evaluated by means of K-K ananlysis and classical oscillator fit.The data were extrapolated below the measured frequency range to estimate the intrinsic microwave losses.The bending and stretching vibration modes of（M,R）-AlO₆ gave primary contributions to the microwave complex permittivity,therefore the distortion of （M,R）O₉ dodecahedra greatly affected the dispersion parameters of these two modes and consequently dominated polarizabilities and intrinsic dielectric losses of MRAlO₄. This could explain the great deviation of measured polarizabilities from those predicted by the oxide additivity law and the variation of calculated Qf values with the tolerance factor.To minimize the intrinsic dielectric loss,it was the keypoint to reduce the distortion of（M,R）O₉ dodecahedra.Moreover,the fact that the calculated Qf values were much higher than the measured ones suggested a great opportunity to improve Qf through optimizing the microstructures.By changing molar ratios among CaO,Sm₂O₃,and Al₂O₃,the effects of secondary phases on mcirostructures and microwave dielectric properties were investigated for CaSmAlO₄-based ceramics.In（2+2x）CaO·（1-x）Sm₂O₃·Al₂O₃（x=-0.10,-0.05,0,0.05, 0.10,0.20）ceramics,Ca₃Al₂O₆ and CaO secondary phases were observed at x＞0,while SmAlO₃ and Sm₂O₃ secondary phases were observed at x≤0.In （2+2x）CaO·Sm₂O₃·Al₂O₃（x=-0.02,-0.01,0,0.02,0.04） ceramics,CaSmAl₃O₇,CaO, and Sm₂O₃ secondary phases were observed at x＞0,while SmAlO₃ secondary phase was observed at x≤0.The secondary phases Ca₃Al₂O₆ and SmAlO₃ decreased the Qf values greatly,whereas CaSmAl₃O₇,CaO and Sm₂O₃ had much weaker minus effects on Qf values.Good microwave dielectric properties were achieved in （2+2x）CaO·Sm₂O₃·Al₂O₃（x=0.02,0.03,0.04） ceramics:ε_r≈19,Qf =120,000～125,300 GHz,τ_f=-10～-9ppm/℃.Modification of CaSmAlO₄ was performed by cosubstitution of Ca on A site and Ti on B site,and Ca_1+xSm_1-xAl_1-xTi_xO₄（0≤x≤0.4） ceramics were prepared and characterized.For Ca_1+xSm_1-xAl_1-xTi_xO₄ phases,as x increased,lattice parameter a increased linearly whereas lattice parameter c decreased linearly;the distortion of （Al,Ti）O₆ octahedra reduced slightly,whereas（M,R）O₉ dodecahedra were further compressed along the c axis,and this was responsible for the decrease in lattice parameter c.Ca_1+xSm_1-xAl_1-xTi_xO₄ ceramics showed very good microwave dielectric properties,especially when 0.06≤x≤0.2（ε_r≈20,Qf=96,500～118,700GHz,andτ_f=-8～2 ppm/℃）.SmAlO₃ secondary phase was detected at x=0,and trace amount of CaTiO₃ secondary phase was detected at x≥0.15;abnormal grain growth was observed in samples with x=0,0.02 and sintering temperature of 1500℃. Suppression of these microstructures would help Ca_1+xSm_1+xAl_1-xTi_xO₄ ceramics maintain high Qf values.With certain amount of excessive CaO in composition, microwave dielectric properties of Ca_1+xSm_1-xAl_1-xTi_xO₄-based ceramics were further improved and excellent microwave dielectric properties（ε_r=20.2,Qf=100,000GH,τ_f=0.5 ppm/℃） were achieved at x=0.15.更多还原