KDP -type crystal

However, Ichikawa et al. [12] found a linear relationship between Tc and Ro-o, which is common to several KDP-type crystals, irrespective of whether they are deuterated or not. This finding suggests that the difference in Ro-o between KDP and DKDP (J o-o = 2.50 A for KDP and Rq-q = 2.52 A for DKDP at room temperature [10]) or the geometric isotope effect, rather than the difference in tunneling frequencies, causes the isotope effect on Tc. 

One can also wonder, which is the original cause of the ferroelectric-para-electric phase transitions in KDP-type crystals the H-hopping or the vibrations (rotations) of the H-bonded molecules. It has been shown that the angular displacements and the H-sites are coupled, thus the vibrations of molecules destabilize and facilitate the H-hopping. This coupling is essential for understanding the interactions between the lattice-mode vibrations in crystals, and the transformations in hydrogen bonds. Also other features of the KDP crystals, like the existence of soft modes, can be explained in this way. 

As already noted, various crystals similar to KDP, where the K-atom or the P-atom of the anion is replaced by homologous atoms, display a similar ferroelectric behaviour. Some of them are antiferroelectrics (41). Recently, some other types of ferroelectrics have been discovered, where the origin of their ferroelectric behaviour is due to the position of the proton itself, which is not the case for KDP-type ferroelectrics where H-bonds are roughly perpendicular to the permanent electric dipole moment fL in the ferroelectric phase and do not directly contribute to the permanent electric moment. Thus such a crystal as... 

The sample fluorescence is time resolved by the upconversion method. The fluorescence is upconverted in a Type II KDP crystal by a portion of the 1064 nm light which travels a fixed path that is portrayed in Figure 1. The "upconverted" light intensity... 

Variations of the above apparatus are used in a number of laboratories. Several experiments utilize a type II KDP crystal to generate the third harmonic at 353 nm instead of the fourth harmonic at 264 nm. To obtain a higher repetition rate at a sacrifice in temporal resolution, the glass laser can be replaced with a mode-locked neodymium YAG laser. 

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