The molecular aspect of ferroelectricity in KDP crystals

Ab Initio Studies of H-Bonded Systems: The Cases of Ferroelectric KH2PO4 and Antiferroelectric NH4H2PO4

“…(46; 48) The mechanism found agrees with the explanation given in Ref. (87), and is also in accordance with the results obtained by another recent first-principles calculation. (89) We have found that the charge redistributions in the the acid proton bridges and phosphates associated with the instabilities in ADP and KDP are very similar.…”

Coexistence of Order–Disorder and Displacive Behavior of KH2PO4 and Analogs from Electron Paramagnetic Resonance

“…They show that the ENDOR measured superhyperfine couplings for KH 2 AsO 4 are: a close =-30 MHz, and a far =-4 MHz cannot be reconciled by any calculation of a simple distance dependence of the "close" and "far" protons. The large variation can be easily understood by recognizing that the proton attachment to an oxygen alters the charge distribution nonlinearly, and leads to the development of the dipole around the central AsO 4 unit, as was suggested earlier by Bystrov and Papova [38].…”

“…Blinc et al [24] thus demonstrated that the four H's undergo a hopping type dynamics in their O -H...O potential wells, at the slow rate of 100 MHz. Subsequently, Dalal et al carried out precise electron nuclear double resonance (ENDOR) measurements and showed that the proton and As motional correlation times are different at high temperatures but they become the same as the temperature approached the phase transition [25,[29][30][31][32][33][34][35][36][37][38][39], which has now become a text-book example of the use of EPR for studying phase transitions [51].…”

“…Much more detailed information has been obtained through electron nuclear double resonance (ENDOR) measurements mainly by Dalal and coworkers, initially using a self-designed spectrometer [16,20,25,[27][28][29][30][31], and later a Bruker system [33][34][35][36][37][38][39]. One significant ENDOR study on protons around the CrO 4…”

“…The present undertaking discusses the utilization of electron paramagnetic resonance (EPR) spectroscopy for investigating dielectric solids that are diamagnetic in their native state, but can be made slightly paramagnetic by lightly doping them with transition ions, such as Fe 3+ , as pioneered by Müller [2][3][4][5][6][7], or by using molecular probes such as the CrO 4 3-(Cr 5+ ) ion [1,[8][9][10][11][12][13], SeO 4 3radical [14][15][16][17][18][19][20][21][22] and the AsO 4 4center [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. While Müller's studies using Fe 3+ as a probe in SrTiO 3 and LaAlO 3 are considered as some of the classic examples of the power of EPR technique in probing microscopic mechanisms of phase transitions in the perovskites [2][3]…”