Temperature coefficient of capacitance

The temperature coefficient of capacitance, denoted a or TCC and expressed in K , is determined accurately by measurement of the capacitance change at various temperatures from a reference point usually set at room temperature (Tj) up to a required higher temperature (Tj) by means of an environmental chamber  

In the electrical industry, the temperature coefficient of capacitance is usually expressed as the percent change in capacitance, or in parts per million per degree Celsius (ppm/°C). Moreover, for industrial dielectrics, it is usually plotted in the temperature range -55°C to +125°C. 

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Special features of mica capacitors are long-term stability (for example, AC/C 0.03% over three years), a low temperature coefficient of capacitance (TCC) (+ 10-80MK-1) and a low tan<5. 

Bukun and Ukshe calculated the integral capacitance from an infinite series, for a multilayer interface by treating the net-charged ionic layers as the plates of a parallel multiplate capacitor. In practice, it was only necessary to consider three layers to approximate the series. They were able to define a set of parameters, derived from the experimentally determined temperature coefficient of capacitance, which enabled them to obtain reasonable verification of their theory as indicated by the agreement between calculated and observed capacitances. 

Capacitor values vary with temperature due to the change in the dielectric constant with temperature change. The temperature coefficient of capacitance (TCC) is expressed as this change in capacitance with a change in temperature. 

The Hg/dimethyl formamide (DMF) interface has been studied by capacitance measurements10,120,294,301,310 in the presence of various tetraalkylammonium and alkali metal perchlorates in the range of temperatures -15 to 40°C. The specific adsorption of (C2H5)4NC104 was found to be negligible.108,109 The properties of the inner layer were analyzed on the basis of a three-state model. The temperature coefficient of the inner-layer potential drop has been found to be negative at Easo, with a minimum at -5.5 fiC cm-2. Thus the entropy of formation of the interface has a maximum at this charge. These data cannot be described... 

The temperature coefficient of conductance is approximately 1-2 % per °C in aqueous 2> as well as nonaqueous solutions 27). This is due mainly to thetemper-ature coefficient of change in the solvent viscosity. Therefore temperature variations must be held well within 0.005 °C for precise data. In addition, the absolute temperature of the bath should be known to better than 0.01 °C by measurement with an accurate thermometer such as a calibrated platinum resistance thermometer. The thermostat bath medium should consist of a low dielectric constant material such as light paraffin oil. It has been shown 4) that errors of up to 0.5 % can be caused by use of water as a bath medium, probably because of capacitative leakage of current. 

In case of a homogeneous temperature distribution in the heated area, h corresponds to the temperature coefficient of the heater material, otherwise h includes the effects of temperature gradients on the hotplate. As a consequence of the aheady mentioned self-heating, the applied power is not constant over time, and the hotplate cannot be simply modelled using a thermal resistance and capacitance. Replacing the right-hand term in Eq. (3.28) by Eq. (3.35) leads to a new dynamic equation ... 

A parallel-plate capacitor at 25 °C comprises a slab of dielectric of area 10 4 m2 and thickness 1 mm carrying metal electrodes over the two major surfaces. If the relative permittivity, temperature coefficient of permittivity and linear expansion coefficient of the dielectric are respectively 2000, — 12MK 1 and 8MK 1, estimate the change in capacitance which accompanies a temperature change of + 5 °C around 25 °C. [Answer — 0.035 pF]... 

There are two ferrite material properties which were not discussed in Section 9.3.1 but which are important in the inductor context they are the temperature and time stabilities of the permeability which, of course, determine the stability of the inductance. The temperature coefficient of permeability must be low, and this has been achieved for certain MnZn ferrite formulations as indicated in Fig. 9.18. A small residual temperature coefficient of inductance can be compensated by a suitable coefficient of opposite sign in the capacitance of the resonant combination. 

In electrical engineering, it is common to classify dielectrics in three main classes. Actually, dielectric materials are identified and classified in the electrical industry according to the temperature coefficient of the capacitance. Two basic groups (Class I and Class II) are used in the manufacture of ceramic chip capacitors, while a third group (Class III) identifies the barium-titanate solid-structure-type barrier-layer formulations used in the production of disc capacitors. 

Important thermoelectrochemical insight has been obtained by investigating the temperature dependencies of a, C and p. The temperature coefficients of a at the electrocapillary maximum, of C at the capacitive minimum and of are important sources for information about the double layer stmcture. The latter depends on temperature dependent changes of physical solution properties (see Sect. 2.5). Classical investigations have been done at ideal polarizable electrodes , i.e. at electrodes where no charge transfer across the interface electrode/solution is occurring during polarisation. Very often, the mercury drop electrode has been used as an example of an ideal polarisable electrode. 

A key factor in the suitabihty of cokes for graphite production is their isotropy as determined by the coefficient of thermal expansion. After the calcined coke was manufactured into graphite, the axial CTE values of the graphite test bars were determined using a capacitance bridge method over a temperature range of 25 to 100°C. The results are summarized in Table 24. Also included in the table are bulk density measurement of calcined cokes and the resistivity values of their graphites. 

Exposure of bulk GaAs Si wafers to a capacitively coupled rf deuterium plasma at different temperatures generates deuterium diffusion profiles as shown in Fig. 1. These profiles are close to a complementary error function (erfc) profile. At 240°C, the effective diffusion coefficient is 3 x 10 12 cm2/s. The temperature dependence of the hydrogen diffusion coefficient is given by (Jalil et al., 1990) ... 

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