Preparation And Electrical Properties Of Bismuth Titanate Lanthanide Humidity Sensitive Element

Humidity sensors have gained plenty of attention in recent years because of their various applications,including environmental,agricultural,industrial,and food sectors.As a core component of humidity sensor,humidity sensing material has a great influence on the performance of the sensor.Hence,numerous researchers devote to exploring new humidity sensing materials and improving the preparation process of humidity sensing materials to obtain high performance humidity sensing material.The BLT powders and BLnT(Ln=La,Ce,Nd,Sm)nanofibers are prepared by the metal-organic decomposition(MOD)method and electrospun method,and the corresponding humidity sensing sensor devices are fabricated in this paper.The humidity sensing properties of BLT powders annealed at different temperatures and bismuth titanate lanthanum series nanofibers are investigated to find out the effect of annealing process and different lanthanide doping on the humidity sensing properties.The work can be divided into the following three parts:1?The BLT precursor solution is synthesized by MOD method.The BLT powders(BLT-350,BLT-450,BLT-550,BLT-650,BLT-750)are eventually obtained by annealing the BLT precursor solution at 350°C,450°C,550°C,650°C and 750°C,respectively,and the corresponding humidity sensor devices are prepared.The BLT powders are characterized by X-ray diffraction(XRD),field-emission scanning electron microscopy(FE-SEM),energy dispersive X-ray spectroscopy(EDX)and specific surface and pore size analysis instrument.The humidity sensing properties of BLT humidity sensors are measured by precision impedance analyzer and humidity generator.Test results are as follows:(1)The optimal working frequencies of all the humidity sensors are 100 Hz.(2)The annealing process has great effect on the humidity sensing properties of BLT powders.The impedance variation of BLT humidity sensor is over more than five orders of magnitude and the sensitive curves has best linearity when the annealing temperature is 550°C,which the impedance variation is only about one order of magnitude for humidity sensors annealed at other temperatures.(3)The response time is about 8 s,and the maximum hysteresis of BLT-550 humidity sensor is around 3% relative humidity(RH).The results indicate that the annealing process has great effect on the humidity sensing properties of BLT powders,and the BLT powder annealed at 550°C is of good humidity sensitive characteristic.The BLT-550 is a promising material for the preparation of high performance humidity sensors.2?The BLnT(Ln=La,Ce,Nd,Sm)nanofibers are synthesized by electrospun method,and the corresponding humidity sensors are prepared.The BLnT nanofibers are characterized by XRD,FE-SEM and X-ray photoelectron spectroscopy(XPS).The humidity sensing properties of BLnT nanofibers humidity sensors are measured by precision impedance analyzer and humidity generator.Test results are as follows:(1)The optimal working frequencies of all the prepared humidity sensors are 10 Hz.(2)The different lanthanide doping has great influence on the humidity sensing properties of Bi4TiO3-like sensing materials,and the impedance variation of BST nanofiber humidity sensor is about six orders of magnitude.The humidity sensitive characteristic of BST nanofiber humidity sensor is better than other BLnT nanofibers humidity sensors,and the sensitive curve is of best linearity.(3)The response time and the recovery time of BST nanofiber humidity sensor are about 4 s,and the maximum hysteresis is around 3% RH.The results indicate that BST nanofiber is of optimal humidity sensitive characteristic due to low Ln-O binding energy.The BST nanofiber humidity sensor is of promising application.3?A signal processing system based on BST nanofiber humidity sensor is built.First of all,the circuit is built in PROTUS according to the connection requirements of the components and then the simulation is carried out.After simulation,the actual component welding and the circuit is connected by the simulation results.After that,the program is write so that the humidity value measured by the sensor can be displayed on the LCD screen.Finally,the measured data is calibrated,and the results indicate that the error is existed due to the limited precision of BST nanofiber humidity sensor,but the error is under 5%RH so that it meet stipulated regulation.