Ferroelectric crystals

Molecular ferroelectric pyridin-2-ylmethanaminium perchlorate with phase transition induced by disorder of perchlorate

“…1 Since its discovery in 1921, ferroelectrics have been widely applied in electric random access memories (FeRAM), infrared detectors, pyroelectric vidicons, remote sensing, nonlinear optical devices, capacitors, and laser frequency converters. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Molecular ferroelectrics, as one class of ferroelectric materials, compared with the traditional inorganic ferroelectric materials, have some advantages, such as easy design, nontoxicity, and exibility. [16][17][18][19][20] The study of ferroelectricity began in 1920 with the research on the special dielectric properties of Rochelle salt by Valasek,21 which was nearly 100 years ago.…”

Thermal hologram fixing in pure and doped KNbO_3 crystals

“…The primary charge carriers in KNbO 3 :LiNaFe were changed from holes to electrons after application of an electric field of approximately 100 V/cm at 180'C for 14 h. After this treatment the crystal still showed the same unusual dynamics without any relevant change in the time constants for the compensating grating and the related activation energy defined in Eq. (8). This shows that the secondary carriers also remained the same after the reduction treatment and, since the fixed gratings were still not erasable, the identification of the secondary carriers as electrons or holes can be excluded.…”

Applications of photorefractive crystals

“…Note also that the minimal change in the controlling electric field A& can produce remarkable (practically arbitrary) deflection of the reconstructed signal wave in this arrangement. As was experimentally demonstrated by Yasuhira et a1 (1977( ), Petrov et a1 (1978 and later by Kewitsch et al (l993), the complicated information-bearing signal waves can also be successively switched (figure 5.1 (6)). This enables utilization of this technique in holographic memory units with electrical retrieval, and, as was shown by Petrov et a1 (1983), for electrical switching of optical fibre communication lines.…”

“…Indeed, the main criterion of saturation of these centres during recording of a set of holograms as considered above is clearly EO> E,,. From equation (2.2) for the average carrier spatial frequency l/A= 1000 In/" in LiNbOJ ( 6 3 3 0 , E,-100 kV/cm) this gives the following value for the neccessaryconcentration of the impurity centres: N D -1 0 " ~m ' ~ (in LiNb0,:Fe the concentration of accepter centres Fe3+ exceeds, usually, the concentration of donor centres Fe2+-see Staebler 1977). Note that such concentration of donor centres can be considered as reasonable for the photorefractive LiNbO,: Fe in question (Alphonse and Phillips 1976).…”