Oxidic semiconductor thermistors

Hydrogen Mercury-mercuric oxide detector cell Exhaled hydrogen monitor Palladium metal oxide semiconductors Thermistor thermal conductivity Mathiot et al. (1992), and Pauss et al. (1990) Collins and Paskins (1987) Pauss et al. (1990) Bjomsson et al. (2001)... 

Thermistors. Thermistors (i.e., thermally sensitive resistors) were developed by Ruben97 and are made of metal oxide semiconductors, whose resistance decreases with increasing temperature, because the thermally excited state is more conductive and populated as the temperature rises. The specific resistance p (Q m) is given approximately by... 

Thermistors are usually made from ceramic metal oxide semiconductors, which have a large negative temperature coefficient of electrical resistance. Thermistor is a contraction of thermal-sensitive-resistor. The recommended temperature range of operation is from -55 to 300°C. The popularity of this device has grown rapidly in recent years. Special thermistors for cryogenic applications are also available [12]. 

Thermistors are specially prepared metal oxide semiconductors that exhibit a strong negative temperature coefficient, in sharp contrast to the weak positive temperature coefficient of RTDs. Nominal thermistor resistance, usually specified for 25°C, ranges from less than 1000 S2 to more than 1 Mf2, with... 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Nonstoichiometric oxide phases are of great importance in semiconductor devices, in heterogeneous catalysis and in understanding photoelectric, thermoelectric, magnetic and diffusional properties of solids. They have been used in thermistors, photoelectric cells, rectifiers, transistors, phosphors, luminescent materials and computer components (ferrites, etc.). They are cmcially implicated in reactions at electrode surfaces, the performance of batteries, the tarnishing and corrosion of metals, and many other reactions of significance in catalysis. ... 

Thermal conductivity detector. The most important of the bulk physical property detectors is the thermal conductivity detector (TCD) which is a universal, non-destructive, concentration-sensitive detector. The TCD was one of the earliest routine detectors and thermal conductivity cells or katharometers are still widely used in gas chromatography. These detectors employ a heated metal filament or a thermistor (a semiconductor of fused metal oxides) to sense changes in the thermal conductivity of the carrier gas stream. Helium and hydrogen are the best carrier gases to use in conjunction with this type of detector since their thermal conductivities are much higher than any other gases on safety grounds helium is preferred because of its inertness. 

Thermistor basedflow-through calorimetric sensors. Enzyme thermistors make the most widely developed type of heat measurement-based sensors. The thermistors are normally used as temperature transducers in these devices. Thermistors are resistors with a very high negative temperature coefficient of resistance. They are ceramic semiconductors made by sintering mixtures of metal (manganese, nickel, cobalt, copper, iron) oxides. Like the two previous groups, thermistor sensors do not comply strictly with the definition of "sensor" as they do not consist of transducers surrounded by an immobilized enzyme rather, they use a thermistor at the end of a small... 

A bolometer has a conducting element whose electrical resistance changes as a function of temperature. Bolometers are fabricated from thin strips of metals, such as nickel or platinum, or from semiconductors consisting of oxides of nickel or cobalt the latter are called thermistors. 

The instrumentation for fabrication of the ET normally employs a thermistor as a temperature transducer. Thermistors are resistors with a very high negative temperature coefficient of resistance. These resistors are ceramic semiconductors, made by sintering mixtures of metal oxides from manganese, nickel, cobalt, copper, iron and uranium. They can be obtained from the manufacturers in many different configurations, sizes (down to 0.1-0.3 mm beads) and with varying resistance values The best empirical expression to date describing the resistance-temperature relationship is the Steinhart-Hart equation ... 

Thermistors are resistance thermometers, where the temperature-sensible element is the semiconductor, and are made of a mixture of different metal oxides. The large resistance of the thermistor enables us to lower substantially its dimensions in comparison to the resistance thermometer. Thermistors are very sensible and give a fast response, which is very suitable for use in small calorimeters. 

Another type of resistance thermometer uses metal oxides, instead of metals it is frequently referred to as a thermistor. Electrical resistance of these metal oxides changes rapidly with even rather small temperature changes. Hence, thermistors are often emplyed to measure small temperature changes such as 1°C to 5 °C. The thermistor proper tends to have low purchase prices. Metal oxides, which are semiconductors, include mixtures of the following oxides nickel, manganese, copper, cobalt, tin, germanium, etc. [1]. 

Resistive materials used in thermometry include platinum, copper, nickel, rhodium-iron, and certain semiconductors known as thermistors. Sensors made from platinum wires are called platinum resistance thermometers (PRTs) and, though expensive, are widely used. They have excellent stability and the potential for high-precision measurement. The temperature range of operation is from -260 to 1000°C. Other resistance thermometers are less expensive than PRTs and are useful in certain situations. Copper has a fairly linear resistance-temperature relationship, but its upper temperature limit is only about 150°C, and because of its low resistance, special measurements may be required. Nickel has an upper temperature limit of about 300°C, but it oxidizes easily at high temperature and is quite nonlinear. Rhodium-iron resistors are used in cryogenic temperature measurements below the range of platinum resistors [11]. Generally, these materials (except thermistors) have a positive temperature coefficient of resistance—the resistance increases with temperature. 

The evaluation of elements valences (charge state of an atom in compound with the ionic type of chemical bond) is especially needed for studying and designing such materials as mixed valence semiconductors based on 3d-transition metal oxides. The preliminary set electron or hole current carrier density in such materials can be created by applying the valence regulation method. Such electroconducting oxide materials are widely used as electrodes of fuel cells and other current sources, gas sensors, electric heating elements, thermistors etc. 

Attempts are still being made to produce improved bolometers operating at or near room temperature. These include vanadium oxide metal-semiconductor transition devices [8.7], bismuth-lead layers [8.8], metallic nickel [8.8a], and aluminium [8.8b], silicon carbide [8.8c], and doped barium titanate ceramic [8.8d] elements. New designs of radiometers and power meters using thermistor bolometers have been described [8.9-11]. Microelectronic techniques have been used to produce fast but sensitive (NEP 10 WHz at 25 MHz and 100 pm wavelengths) uncooled for improved bolometers [8.11a]. 

The operation of CTT thermistors is based on the occurrence of a Mott transition in the oxide. The electrical conductivity is a step function. Below the critical temperature the material is a semiconductor or an insulator above this transition temperature the material is a metallic conductor. VO2 is used for this type of thermistor. 

NTC thermistors are doped polycrystalline oxides that have the temperature-dependent conductivity of a semiconductor. NiO doped with Li" is a p-type semiconductor with hopping electron holes (see Chapter 10) and Fe203 doped with Ti an n-type semiconductor that has a conductivity that strongly depends on the... 

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... 

Semiconductor thermometers can be built in many shapes. Frequently they are very small beads, so that their heat capacity and thermal lag are small. They may also be made in form of large disks, so that they can average the temperature over a larger object. Typical materials which are used in thermistor thermometers are iron oxide, magnesium chromate, magnesium aluminate or sintered mixtures of nickel oxide, manganese oxide and cobalt oxide. 

Simple thermocouples are not sensitive enough to detect variations in enzymatic reaction enthalpies. Thermistors and thermopiles can, however, detect such small variations in temperature. Thermistors are mixtures of metallic oxides and polycrystalline semiconductors. The high resistivity values of these materials gives a rapid response time owing to their small size and reduced calorific capacity. TTie resistance R of a thermistor is a function of temperature, T, according to the following expression ... 

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