The Effect Of ZnO On The Microstructure And Electrical Properties Of Mn-Co/Ni-Cu-O NTC Thermistors

It is important that Negative Temperature Coefficient?NTC?resistance is exponentially decreasing resistance with increasing temperature.Those materials are widely used for temperature examination,command and compensation in household electrical appliance,manufacturing industries,healthcare and automotive industry.These materials are widely used in temperature examination,command and compensation in household electrical appliance,manufacturing industries,healthcare and automotive industry via their rapid response,lowest price,convenience and high sensitivity of temperature.Single-phase,homogeneous,fine-grained ceramics with sufficient density are the most advantageous for practical uses.Since the copper oxide can cause significant reduction in resistivity,ternary systems of Mn–Cu–Co and Mn–Cu–Ni oxides,and quaternary systems of Cu–Ni–Co–Mn oxide have become optimal choices of NTC ceramics,We choose Mn–Cu–Co and Mn–Cu–Ni ternary system of NTC thermistor as the research object and adjust the ceramics to a best stability via Zn doping.High stability thermistors are prepared by comparison with different doping content.In this study,we fabricated Mn_1.5-xCo1.2Cu_0.3Zn_xO₄?0?x?0.5?and Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?NTC thermistors via a solid-state reaction and investigated their electrical properties.The performance of powder and ceramics samples were characterized and anyalyzed by TG-DSC,XRD,SEM,and electrical measurement.This thesis can be summarized as follows:?1?The effect of zinc content on the microstructure and properties of Mn_1.5-xCo_1.2Cu_0.3Zn_xO₄?0?x?0.5?thermistors was investigated.According to the XRD test results,it can be seen that the Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?series of thermal ceramic precursor calcined at 900°C,will not change the original spinel phase due to the addition of Zn elements.By comparative analysis of the SEM micro-morphology,it was found that when x=0.3,the series of thermal ceramic materials have uniform grain size,compact arrangement,and high density.?2?After analysis of the results of the electrical performance test,as the doping amount x of Zn increases from 0 to 0.2,the resistivity gradually decreases from206.1907?·cm to 126.6346?·cm,and the material coefficient B value decreased from3464k to 3323k.As the doping amount x of Zn increases from 0.3 to 0.5,the resistivity rapidly increases from 176.1518?·cm to 706.506?·cm,and the material coefficient B value increases from 3427k to 3714k.According to the result analysis,when the doping amount of zinc is 0.2,the material coefficient and the resistivity are obtained as the minimum value.?3?It can be analyzed from the data of XPS that the increase of the thermistor resistivity of Mn_1.5-xCo_1.2Cu_0.3Zn_xO₄?0?x?0.5?is due to the addition of Zn occupied the A-site.That lead to the Mn³⁺and Mn⁴⁺ion pair decreases while at the same time causing a increase in resistivity.?4?MnCo_1.2Cu_0.3Zn_0.5O₄ and Mn_1.5Co_1.2Cu_0.3O₄ thermal sensitive ceramic materials were aged at 125°C for 500 hours.By comparing the data after aging,the aging performance of Mn_1.5Co_1.2Cu_0.3O₄ thermosensitive ceramic materials without zinc addition was better,and it was verified again that the addition of zinc to the copper-containing thermosensitive ceramic materials can improve the thermal stability of the material.?5?The Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?NTC ceramics were prepared by the traditional solid state reaction method.Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?series thermistors were prepared by oxide solid-phase ball milling.After XRD results of Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?series thermistors,As the doping amount of zinc element increases from 0.1 to 0.5,the addition of zinc does not change the original spinel structure of Mn-Ni-Cu-O series thermistors.?6?The effect of different zinc content on the grain distribution of the series of thermal ceramic materials was investigated by microscopic morphology analysis.The results showed that when the doping amount of zinc is 0.4 and 0.5,the denseness of the series thermistors Mn1.5-xNi1.2Cu0.3ZnxO4?0?x?0.5?is improved,and the grains tend to be uniform.Because zinc preferentially occupies the tetrahedral site,there are too many copper element separated in the grains.?7?The temperature-resistance curve of Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?series of thermosensitive materials shows that the resistivity of the system thermosensitive materials has a good linear relationship with the corresponding temperature,which has obvious NTC features.The resistivity and material coefficient of the Mn_1.5-xNi_1.2Cu_0.3Zn_xO₄?0?x?0.5?series of thermosensitive materials show a trend of decreasing firstly and then increasing with the content of zinc.When the doping amount of zinc is 0.1,both resistivity and materials are the minimum values.