Negative Temperature Coefficient NTC Thermistors

Despite the many investigations of the defect chemistry of lithium-oxide-doped nickel oxide, the real nature of the defect structure still remains uncertain. For many years the holes were regarded as being localized on Ni2+ ions to form Ni3+, written Mi -  

every Li+ on a Ni2+ site in the lattice results in the formation of a Ni3+ ion elsewhere. However, an increasing number of studies suggest that the hole may be preferentially trapped on an oxygen ion, thus  

The mechanism of generation of the mobile charge carriers follows that described in the previous two sections. Donor doping is expected to result in ra-typc thermistors. The situation in which Fe203 is doped with TiC 2, analogous to the situation outlined above for TiC 2-doped Cr203, provides an example. The favored mechanism is the formation of electrons, comparable to Eq. (8.1)  

Acceptor doping, as in lithium oxide doping of nickel oxide, produces p-type thermistors. The situation in nickel-oxide-doped Mn304 is similar but slightly more complex. This oxide has a distorted spinel structure (Supplementary Material SI), with Mn2+ occupying tetrahedral sites and Mn3+ occupying octahedral sites in the crystal, to give a formula Mn2+[Mn3+]204, where the square parentheses enclose the ions in octahedral sites. The dopant Ni2+ ions preferentially occupy 

The holes can be regarded a localized on Mn3+ ions to give Mn4+, and the doped oxide has a nominal formula Mn2+[Mn2iJC Mn4 1 Ni2+]04. The material is a p-type semiconductor. 

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Several kinds of conduction mechanisms are operative in ceramic thermistors, resistors, varistors, and chemical sensors. Negative temperature coefficient (NTC) thermistors make use of the semiconducting properties of heavily doped transition metal oxides such as n-ty e Ti O andp-ty e... 

Barium titanate can be made into an w-type semiconductor by heating in a vacuum. Such materials do not exhibit the PTC effect. [Materials heated in vacuum show negative temperature coefficient (NTC) thermistor behavior see Chapter 8]. Samples for use in PCT thermistors are heated in oxygen to prevent any chance of reduction. 

How do negative temperature coefficient (NTC) thermistors respond to temperature changes ... 

The negative temperature coefficient (NTC) thermistors are semiconductive materials whose resistance decreases with increasing temperature as shown in Figure 2.1.6 with other thermistors. Temperature dependence of resistance is given by... 

Common thermistors are based on semiconductors whose resistance decreases significantly as the temperature increases. Currently, thermistors are manufactured from many different materials including polymers and other ceramics and their resistance may either increase with temperature (positive temperature coefficient—PTC) or decrease with temperature (negative temperature coefficient— NTC). The conductivity of pure metals increases with increasing temperatures and instruments based on metals are referred to as RTDs. 

Thermistors. These are semiconductor resistances with temperature coefficients sufficiently high to make them suitable for use in temperature measurement. Many semiconductors have negative temperature coefficients (NTC), which means that their resistance decreases with increasing temperature. Thermistors with reproducible temperature coefficients are difficult to produce, and self-healing within the sensor is always a problem. On the other hand, thermistors are usually both inexpensive and sensitive, and they can be used over a wide temperature range (0-l000°C). 

Thermistors are temperature-dependent resistances, normally constructed from metal oxides. The resistance change with temperature is high compared with the metallic resistances, and is usually negative the resistance decreases with temperature increase. The temperature characteristics are highly nonlinear. Such thermistors, having a negative temperature coefficient, are called NTC thermistors. Some thermistors have a positive temperature coefficient (PTC), but they are not in common use for temperature measurement. 

Thermistors Thermistors are nonlinear temperature-dependent resistors, and normally only the materials with negative temperature coefficient of resistance (NTC type) are used. The resistance is related to temperature as... 

Battery manufacturers and sellers employ external safety devices in the battery package to surmount these problons an Negative Temperature Coefficient sensor (NTC) thermistor has been used as an overcurrent interrupter, and Charge Protection... 

Thermistors are resistors with a temperature-dependent value of their resistance. There are three types of thermistors CTT (critical temperature thermistors), NTC (negative temperature coefficient), and PTC (positive temperature coefficient) thermistors. Their thermal behavior is shown in Figure 9.7. 

Negative temperature coefficient resistors, also called thermistors, have a negative temperature dependence in the order of several percent per degree Celsius. They are made from polycrystaUine semiconductors, consisting of oxides of chromium, manganese, iron, cobalt, and nickel. The resistance of a NTC resistor can be expressed as... 

Thermistors cover a temperature range from -80 °C to +350 °C, and have either a negative (NTC) or positive (PTC) temperature coefficient. Typical resistance ranges from around 100Q up to the megaohm (MQ) region. Their response is related... 

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