DEVELOPMENT OF RELAXOR SYSTEM PIEZOELECTRIC SINGLE CRYSTAL OSCILLATOR WITH WIDE PRACTICAL TEMPERATURE RANGE

近几年来，准同型相界（MPB）附近的铅基复合钙钛矿型弛豫铁电体和正常铁电钛酸铅体系的固溶体单晶受到了广泛的关注。这些材料利用畴工程表现出上级压电性能，在超声成像，无损检测（NDT）和致动器的应用。PZN-PT单晶在菱形相中沿沿着[ 100 ]轴的纵杆模式下显示出大的压电常数和大的机电耦合常数。而在MPB附近的P_2N-PT直角晶体的缺点之一是居里温度Tfc较低，为170-180℃。低Tb限制了其工作温度范围UP <85℃，因此，具有大机电耦合因子的新单晶有望获得> 250℃的高Tc。钛酸铟铅（PIN-PT）属于弛豫PT体系，其Tc高于250℃。本文采用助熔剂法在MPB附近生长了PIN-PT单晶，并<33>利用沿[ 100 ]轴沿着方向的菱形槽形PIN-PT单晶，获得了矩形棒模式下的机电耦合系数k_ ' = 78%的相控阵超声换能器。k_<33>'= 78%，是目前所报道的Tc高于250℃的压电材料中的最高值.研究<33>了极化态和非极化态的k '随温度的变化关系。随着温度的升高，k <33>'略有下降，在200℃时仅下降5%.这样的温度特性对于实际应用是相当有吸引力的。此外，通过更可重复和更实用的布里奇曼法，成功地生长了PIN-PT单晶，以及助熔剂法。

Recently much attention has been given to single crystals of solid solutions of lead-based complex perovskite relasor ferroelectrics and normal ferroelectric lead titanate systems near the morphotropic phase boundary( MPB ). These materials exhibit superior piezoelectric properties by utilizing domain engineering, for applications in ultrasonic imaging, nondestructive testing( NDT ) and actuators. The PZN-PT single crystal shows a large piezoelectric constant and large electromechanical coupling constant in the longitudinal bar mode along the [ 100 ] axis in the rhombohedral phase. However one ofthe disacfeatages rfeangle crystals P2N-PT near the MPB is their tow Curie temperature Tfc of 170-180℃. The low Tb restricts tihe operating temperature range UP to less than 85℃.Therefore, a new single crystal which has a large electromechanical coupling factar with a high Tc> 250℃ is anticipated. Lead indium niobate lead titanate ( PIN-PT ) belongs to one of the relaxer-PT systems with Tc higher than 250℃. In this work, PIN-PT single crystals near the MPB were grown successfully by a flux method The electromechanical coupling factor in rectangular bar mode k_<33>' = 78 % fax phased array ultrasonic transducers was obtained by using the rhomboherdal PIN-PT singfe oystal cdented along [ 100 ] axis. The k_<33>'= 78 % is the highest value reported so far among all piezoelectric materials with Tc higher than 250℃. The temperature dependence of the k_<33>' was investigated in poled and unpoled states. With increasing temperature, the k_<33>' decreases slightly and even at 200℃ decreases by only 5 %. Such temperature characteristics is quite attractive for practical applications. Moreover, by the more reproducible and more practical Bridgman method, PIN-PT single crystals were successfully grown, as well as a flux method.