JPH01239802A - Thermistor - Google Patents

Abstract

PURPOSE:To obtain a thermistor having excellent reliability as a sensor by forming it of sintered mixture of metal oxides, incorporating a total of 100atomic% of Co, Cu and Li as three types of component metal elements, a specific atomic % or more of the content of the Li being in solid solution in crystal grains of NaCl type cobalt oxide. CONSTITUTION:Sintered mixture of metal oxides is contained, a total of 100atomic% of three types of Co, Cu and Li are contained as component metal elements, and at least 85atomic% or more of the content of the Li is contained in solid solution in the crystal grains of NaCl type cobalt oxide. For example, cobalt nitrate, copper nitrate and lithium carbonate are employed as starting materials, dissolved to obtain a ratio of Co:Cu:Li=80:3:17atomic%, evaporated, dried to be solidified, temporarily baked at 600 deg.C, and the baked material is wet pulverized in a ball mill. After its slurry is dried, polyvinyl alcohol is added and mixed as a binder, a predetermined quantity is metered, and pressure molded in a disc state to form a molded piece. The piece is baked at 1200-1300 deg.C in a nitrogen gas flow for 2 hours, and electrodes are provided on both side faces of the sintered material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermistor having a large negative temperature coefficient of resistance and which can be used as a highly responsive and highly accurate temperature sensor.

Conventional technology Conventionally, oxide semiconductors made by combining cobalt oxide and lithium have been developed using the old (V
Covered by Arway et al. (Philips
Re5search Report 6173 (19
50)).

However, the study by Verwey et al. was only at an academic stage, and the solid solution amount of lithium was 1 wt % or less, which was before the development of use as a thermistor.

In Japan, two reports [■Hitachi,
A collection of papers commemorating the 20th anniversary of the founding of the Central Research Institute.

p30-46. 1961], but the thermistor characteristics are low in both specific resistance and B constant, and are not suitable as a thermistor, but are described as similar to this.

On the other hand, as a result of re-examination by the present inventors, an excellent thermistor material with a low specific resistance and a high B constant can be obtained by combining cobalt oxide and lithium with a specific crystal structure. I found out that it can be done. Furthermore, it has been found that a material to which copper is added also has excellent thermistor characteristics.

Problems to be Solved by the Invention The above-mentioned thermistor material exhibited the best characteristics in a composition range containing 0.5 to 2 atomic percent lithium with respect to cobalt 2 and copper. In other words, conventional cobalt and manganese can be used as disc thermistors even when left at a high temperature of 150'C.

Even compared to spinel crystal type thermistors made of transition metal oxides whose main components are copper and nickel, very stable results were obtained. However, in DC load tests, especially DC load tests in direct current, they have a problem in that they are not as good as conventional general-purpose thermistors. As a result of analyzing the cause of this defect, it was determined that lithium, which was thought to be solidly dissolved in cobalt oxide, segregates at grain boundaries or crystal junctions, and lithium ion / moves due to DC load. .

The present invention solves these problems and aims to provide a thermistor that is highly reliable as a sensor.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention, as a result of various improvement studies, consists of a sintered mixture of metal oxides,
Its constituent metal elements include cobalt (Co), copper (Cu
) and lithium (Li) in a total of 100 atom% f
The present invention is characterized in that a lithium content of at least 85 atoms or more is dissolved in crystal grains of NaCg-type cobalt oxide.

Function: By satisfying this ceramic microstructure, it exhibits better stability than conventional thermistors even in DC load tests and mixed load tests.

Example An embodiment of the present invention will be described below.

First, using commercially available cobalt nitrate, copper nitrate, and lithium carbonate as starting materials, Go:Cu:Li=sO:3:
The mixture was dissolved to a ratio of 17 atoms, evaporated to dryness, and then calcined at a temperature of 600°C, and the calcined product was wet-pulverized in a ball mill. After drying this slurry, add and mix polyvinyl alcohol as a binder, take the required amount and pressure mold it into a disk shape to make a number of molded products. did. A on both sides of the disk-shaped sintered body thus obtained.
An electric kettle containing g as a main component was provided and used as a sample. In the above process, several types of samples were prepared by changing the slurry drying method 1 condition and firing condition.
During H, tests were conducted with a direct load (2000 hours) at a load power of 0.4 W (7) and high temperature storage at 150° C. (20 degrees Celsius hours). In addition, elemental analysis of the device was performed using atomic absorption spectroscopy, dividing the device into device components and eluted components. The results are summarized in the table below.

As a result of confirming the crystal structure of these shredded samples by X-ray diffraction, Na1l type cobal oxide (Coo) was identified.

(Margin below) (The black mark is a comparative example and is outside the scope of claims) In this table, the value shown in the granule section of the lithium content is the total amount minus the elution amount. The value shown in the section for boundaries (grain boundaries and joints) is the amount of eluted components. Here, as for the product specifications of the thermistor, since the resistance value change rate in the humidity load test is within 15%, samples 14A and B in the table above are
will be satisfied. That is, if 85 atoms or more of lithium is dissolved in the crystal grains of NaC77 type hycobalt, the specifications can be fully satisfied.

In addition, the specific resistance and B constant of these samples (26°C and 50°
(based on the resistance value of C) were both 970Ω・Cnf minus 10%, B constant M=4620(k)±3 coefficient.

Here, cobalt has 73.0 to 99.4 atoms, and copper has 0
．． 1-7. ○It is preferable that lithium has a composition in the range of 0.5 to 20.0 atoms to satisfy the requirements of low resistivity, 1 high B constant, and better meet the electrical characteristics required by the device side as a sensor. can be even more fulfilling. This is as previously disclosed by the present inventors in Japanese Patent Application No. 132427/1982.

Effects of the Invention As described above, the present invention provides a thermistor that has a low specific resistance, a high B constant, and a negative temperature coefficient of resistance, and is excellent in reliability even in high temperature storage tests and humidity load tests. However, it can be used as a sensor with high accuracy, high responsiveness, and high reliability, and is expected to have new applications.

Claims (1)

[Claims] It consists of a sintered mixture of metal oxides, and its constituent metal elements include cobalt (Co), copper (Cu), and lithium (
What is claimed is: 1. A thermistor comprising a total of 100 atomic % of three types of Li), and at least 85 atomic % or more of the lithium content is dissolved in crystal grains of NaCl-type cobalt oxide.