Research On Preparation And Properties Regulation Of NTC Thermosensitive Ceramic Materials With Perovskite Structure

Negative Temperature Coefficient（NTC）thermistors are widely used in devices such as temperature measurement,control,compensation and voltage regulation due to their fast response,high sensitivity and small size.Perovskite-type NTC thermosensitive ceramics are considered to be one of the main candidate materials for new NTC thermistors due to their excellent high temperature structural stability,and are also a hotspot in the research of new NTC thermistor materials in recent years.In this study,a series of perovskite NTC thermosensitive ceramics were prepared by solid-state reaction method,the effects of element doping and multiphase composite on their structure and electrical properties were studied,and the impedance behavior and conduction mechanism were also analyzed.The main research results are as follows:1.Cr2O3 and Ho2O3 doped CCTO-based NTC thermosensitive ceramics were prepared by solid-state reaction method.The results showed that all CCTO-based ceramic samples exhibited a cubic perovskite structure.The doping of Cr2O3 and Ho2O3 both suppressed the abnormal growth of grains and significantly improved the inhomogeneity of grain size.With the increase of Cr2O3 doping content,the resistivity（ρ25）decreased from8.18×10⁶ to 1.24×10⁶Ωcm,and the B25/75 decreased from 6573 to 4542 K.Ho2O3 doping reduced theρ25 from 7.54×10⁶ to 1.64×10⁵Ωcm,and the B25/75 range was 4425-6196 K.XPS results showed the coexistence of Ti⁴⁺/Ti³⁺and Cu²⁺/Cu⁺in CCTO-based ceramics,indicating that the electrical conductivity originates from the electron hopping mechanism.Simultaneously,Cr³⁺and Ho³⁺were doped as donor ions to introduce more electrons,which increased the concentration of heterovalent ion pairs and reduced the resistivity.The fitting results of impedance spcctra showed that both grains and grain boundaries contribute to the NTC behavior.2.Y2O3 and Gd2O3 doped BBF-based NTC thermosensitive ceramics were prepared by solid-state reaction method.The results showed that the main phase of all BBF-based ceramic samples was tetragonal perovskite structure,and appropriate amount of Y2O3 and Gd2O3 doping promoted the grain growth.All BBF-based ceramics exhibited the typical NTC effect,and XPS confirmed the coexistence of Fe²⁺and Fe³⁺ions,which could attribute the conductivity of BBF-based ceramics to the electron hopping mechanism.Theρ25,B25/75 and Ea of（1-x）BBF-x Y2O3 ceramics and（1-x）BBF-x Gd2O3 ceramics ranged from4.19×10⁶-7.82×10⁷Ωcm,6441-7611 K,0.5003-0.5529 e V and 4.70×10⁵-4.72×10⁶Ωcm,5573-6697 K,0.4778-0.5680 e V,respectively.The impedance analysis results showed that the grain boundary resistance of BBF-based ceramics was higher than the intragranular resistance,and all samples had a single relaxation process.3.x YCM-（1-x）CCTO)and BT-BF-x La2O3 composite perovskite type ceramics were prepared by solid-state reaction method.All composite ceramics exhibited good NTC effect.The main phase of x YCM-（1-x）CCTO ceramic samples was cubic perovskite structure.When x（29）0.04,the grain size decreasesd and the distribution became more inhomogeneous with the increase of YCM content.The range ofρ25,B25/75 and Ea of the samples were 2.21×10⁶-7.30×10⁶Ωcm,5797-6300 K,0.5390-0.5800 e V,respectively.For BT-BF-x La2O3 composite ceramics,La2O3 doping suppressed abnormal grain growth and reduced grain size.ρ25,B25/150 and Ea ranged from 4.59×10⁶-3.51×10⁸Ωcm,2753-3360 K and 0.2347-0.3023 e V,respectively.All ceramic samples exhibited electrical relaxation,which was attributed to the formation and ionization of oxygen vacancies.