Tantalate, lithium

There is often a wide range of crystalline soHd solubiUty between end-member compositions. Additionally the ferroelectric and antiferroelectric Curie temperatures and consequent properties appear to mutate continuously with fractional cation substitution. Thus the perovskite system has a variety of extremely usehil properties. Other oxygen octahedra stmcture ferroelectrics such as lithium niobate [12031 -63-9] LiNbO, lithium tantalate [12031 -66-2] LiTaO, the tungsten bron2e stmctures, bismuth oxide layer stmctures, pyrochlore stmctures, and order—disorder-type ferroelectrics are well discussed elsewhere (4,12,22,23). 

DTGS = deuterated triglycine sulfate KRS — 5 = mixed thallium bromide-iodide LT = lithium tantalate MCT = mercury cadmium telluride and OPO = optical parametric oscillator. 

The second group is the group of oxyfluorides that are derived from ferroelectric oxides by means of fluorine-oxygen substitution. The basic oxides are usually perovskite, tetragonal tungsten bronze, pyrochlore, lithium tantalate etc. [400]. 

Another method of raw material decomposition is based on the fluorination of the raw material by the hydrofluoride method. No published data exists on hydrofluoride decomposition of columbite or tantalite concentrates. The interaction can, nevertheless, be discussed based on available information on the decomposition of lithium tantalate, LiTaC>3, and lithium niobate, LiNb03, using the hydrofluoride method [113,118,122]. 

The chemical interaction of lithium tantalate with molten ammonium hydrofluoride can be represented as follows ... 

Lithium niobate decomposition, 264 formation mechanism, 35-37 Lithium tantalate decomposition, 263 formation mechanism, 35-37 LO-TO splitting, 242... 

Sources and detectors Specific discussions of sources and detectors have been covered elsewhere in this article. The issues here are more service and performance related. Most sources have a finite lifetime, and are service replaceable items. They also generate heat, which must be successfully dissipated to prevent localized heating problems. Detectors are of similar concern. For most applications, where the interferometer is operated at low speeds, without any undesirable vibrational/mechanical problems, the traditional lithium tantalate or DTGS detectors are used. These pyroelectric devices operate nominally at room temperature and do not require supplemental cooling to function, and are linear over three or four decades. 

Current detectors use a deuterated triglycerine sulphate (DTGS) crystal or lithium tantalate (LiTa03) sandwiched between two electrodes from which they receive the radiation. This allows monitoring of the rapid modulation of the radiation intensity. Under the effect of a potential difference, the crystal becomes pyroelectric. It is polarised and acts as a dielectric whose degree of polarisation varies with the... 

Figure 1.9 Reciprocal dielectric susceptibility at the phase transition of lithium tantalate (second order phase transition) and of barium titanate (first order phase transition).

The dielectric behavior closed to a phase transistion is displayed in Figure 1.9 for barium titanate (first-order transition with Tc = 135°C, C = 1.8 105oC) and for lithium tantalate (second-order transition with Tc = 618°C and C = 1.6 105 °C). 

Lithium tantalate is a single-crystal material that is produced in quantity by the Czochralski method (see Section 3.11) for piezoelectric applications and is therefore readily available. It is stable in a hard vacuum to temperatures that allow outgassing procedures. It is insensitive to humidity. It is widely used where precise measurements are to be made. 

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