摘要:近年来，随着人们对生存环境的关注逐渐增加，无铅压电材料的研究逐渐成为压电材料领域的研究热点。钛酸铋钠基无铅压电材料被认为是最有希望取代铅基的压电材料。采用顶部籽晶助溶剂提拉法（TSSG）生长出具有良好的压电性能、机电耦合系数的0.14 at% Mn掺杂的0.95(Na1/2Bi1/2)TiO3-0.05BaTiO3（0.95NBT-0.05BT）单晶。X射线粉末衍射表明，该方法生长的单晶室温下是三方相结构。随着温度的升高，Mn掺杂的0.95NBT-0.05BT单晶发生系列的结构相变：室温-230℃呈现三方相结构，530℃转变为四方相，580℃时转变为立方相。Mn掺杂的0.95NBT-0.05BT单晶呈现复杂的电畴组态，室温下呈现统计四次对称性。红外光谱测试表明，在630cm-1、1300cm-1左右存在红外吸收峰。拉曼光谱测试表明，在300cm-1，570cm-1，800cm-1出现三个弥散的拉曼峰，分别对应[TiO6]的扭曲模，[TiO6]的拉伸模和“软模”。室温下，(111)取向的单晶介电常数、介电损耗最大。极化前(110)切型的单晶的介电性能接近弛豫铁电体，(001)、(111)切型的单晶的介电性能接近正常铁电体。极化后单晶的相对介电常数总体上减小，极化后单晶的介电性能更加接近正常铁电体。Mn掺杂的0.95NBT-0.05BT单晶呈现典型的电滞回线，随着频率的降低和电场强度的增加，电滞回线由窄而狭长的形状向宽而接近矩形的形状转变，伴随着剩余极化强度和矫顽场的增大。(001)取向的单晶呈现出最佳的压电性能，d33值达到233.4pC/N。随着温度升高，Mn掺杂的0.95NBT-0.05BT单晶的压电常数、机电耦合系数基本不变，130℃以上，压电常数、机电耦合系数迅速减小。(110)取向的单晶具有相对较好的热释电性能：p值为935.7µC/K·m2，Fi值为3859.4pm/V，Fv值为0.347m2/C，Fd值176.6µPa-1/2。
关键词：Mn掺杂的0.95NBT-0.05BT单晶；晶型转变；介电性能；压电性能；铁电性能；热释电性能
Abstract:In recent years, with the increase of environmental concerning, the researches about lead-free piezoelectric materials have become a hotspot in the field of piezoelectric materials. Sodium bismuth titanate based lead-free piezoelectric materials are regarded as the most promising candidates for the lead-based piezoelectric materials so far. 0.14 at% Mn-doped 0.95(Na1/2Bi1/2)TiO3-0.05BaTiO3 (0.95NBT-0.05BT) lead-free single crystals with excellent piezoelectric and electromechanical coupling properties were successfully grown by a top-seeded solution growth method (TSSG). X-ray powder diffraction measurement showed that the as-grown crystal possesses trigonal crystalline structure. With the increase of temperature, successive structural phase transitions occur in the Mn-doped 0.95NBT-0.05BT single crystals. The single crystals exist in trigonal phase between room-temperature and 230℃, which change to tetragonal phase at 530℃, and then change to cubic phase above 580℃. The Mn-doped 0.95NBT-0.05BT single crystals exhibit complex domain configuration with statistical symmetry. The infrared-absorption bands occurr around 630cm-1 and 1300cm-1 observed by the fourier transform infrared spectroscopy (FT-IR) spectra. Three diffused Raman bands center around 300cm-1, 570cm-1 and 800cm-1 observed by the Raman scattering spectroscopy, which can be attributed to the [TiO6] vibration, [TiO6] stretching and “soft mode”. (111)-oriented Mn-doped 0.95NBT-0.05BT crystal planes exhibit the largest values of dielectric constant and dielectric loss. Before poling, the dielectric response character of the (110)-oriented Mn-doped 0.95NBT-0.05BT crystal planes is similar to that of relaxor ferroelectrics, while as the (001)- and (111)-oriented Mn-doped 0.95NBT-0.05BT crystal planes is similar to that of normal ferroelectrics. After poling, the dielectric behavior of all orientations of the single crystals approaches more to normal ferroelectrics accompanied by the decrease of the value of dielectric constant. The Mn-doped 0.95NBT-0.05BT single crystals exhibit typical P-E hysteresis loops, where the shape of the P-E loops changes from narrow to nearly rectangular shape with the decrease of frequency and the increase of electric field, accompanied by the increase of remnant polarization and coercive field. The (001)-oriented Mn-doped 0.95NBT-0.05BT single crystals exhibit the excellent piezoelectric properties, in which the value of d33 is 233.4pC/N. The values of d33 and electromechanical coupling coefficient Kp maintain almost unchangeable, which decrease greatly above the depolarization temperature Td of 130℃. The (110)-oriented crystals exhibit the best pyroelectric properties, in which the values of p, Fi, Fv and Fd are 3859.4 pm/V, 935.7µC/K·m2, 0.347m2/C and 176.6µPa-1/2, respectively.
Keywords: Mn-doped 0.95NBT–0.05BT single crystals; structural phase transition; dielectric properties; piezoelectric properties; ferroelectric properties; pyroelectric properties
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