Single Crystal Growth and Domain Control of Potassium Niobate Crystals by Vertical Bridgman method

铌酸钾（KNbO_3：KN）是一种压电材料，具有很大的压电常数和机电耦合系数。因此，KN有望成为未来取代含铅压电陶瓷的压电材料之一，并且作为使用表面声波的宽带滤波器器件的基板也引起了人们的关注。然而，KN是一种不一致熔化的材料，因此，人们普遍认为，KN单晶只能通过溶液生长，即顶部籽晶溶液生长（TSSG）方法生长。在我们以前的研究中，我们表明，直径为10毫米的KN单晶可以用垂直布里奇曼（VB）法生长。本研究采用VB法生长了直径为1英寸的KN单晶，并对生长的KN晶体的电性能进行了研究。将粉末状K2 CO 3和Nb 2 O 5按K2 CO 3：Nb 2 O 5 = 52.5：47.5mol%的比例混合，压缩并煅烧混合物。将所得的柱化化合物用作原料。以Z方向的KN单晶为籽晶，在空气中用VB法生长出直径为1英寸的RN晶体。生长使用铂坩埚，生长速度为0.5mm/h。生长后，晶体在其相变温度附近缓慢冷却。将晶体切割成晶片并抛光，并通过X射线形貌术检查晶片。极化处理后，用阻抗分析仪对极化后的VB-KN样品的压电性进行了评价。结果表明，采用VB法生长出了云雾状多畴KN晶体。通过X射线形貌分析证实，生长的晶体几乎是单晶。极化过程后，VB生长的KN单晶显示出与TSSG法生长的晶体相似的压电性。

Potassium niobate (KNbO_3: KN) is known as a great piezoelectric materials which has large piezoelectric constant and electro-mechanical coupling coefficient. Therefore, KN is expected to be one of the future piezoelectric materials instead of lead-containing piezoelectric ceramics, and it has also been attracting attention as the substrate of filter devices with wide band using surface acoustic wave. However, KN is an incongruent-melting material, therefore, it is widely believed that a KN single crystal can be only grown by solution growth that means the top-seeded solution growth (TSSG) method. In our previous study, we showed that KN single crystals 10 mm in diameter could be grown by vertical Bridgman (VB) method. In this study, growth of KN single crystal 1 inch in diameter was demonstrated by VB method and the electric properties of the grown KN crystal was investigated.Powdered K_2CO_3 and Nb_2O_5 were mixed in a ratio of K_2CO_3 : Nb_2O_5 = 52.5 : 47.5 mol%, and the mixture was compressed and was calcined. The resulting columned compounds were used as the raw materials. A z-directional KN single crystal was used as the seed, RN crystals 1 inch in diameter were grown by VB method in air. A platinum crucible was used for the growth, and the growth rate was 0.5 mm/h. After the growth, the crystal was cooled slowly near temperatures of its phase transformation. The crystals were cut into wafers and polished, and the wafers were examined by X-ray topography. After the polarization process, the piezoelectricity of the polarized VB-KN samples was evaluated by using impedance analyzer. As the results, cloudy multi-domain KN crystals were grown by VB method. It was confirmed by X-ray topography that the grown crystals were almost single crystal. After the polarization process, the VB-grown KN single crystal revealed piezoelectricity similar as that grown by TSSG method.