Phase transitions in nanostructured K1-x(NH4)(x)H2PO4 (x = 0 – 0.15) solid solutions

Abstract

Effect of ammonium dihydrogen phosphate admixture on phase transitions in nanostructured solid solutions (1 − x)KH 2 PO 4 -(x)(NH 4 )H 2 PO 4 at x = 0, 0.05 and 0.15 has been studied by dielectric spectroscopy. The samples have been prepared by embedding of aqueous solutions into porous borosilicate glasses. The X-ray diffraction have shown that the crystal structure at room temperature corresponds to the bulk KDP and the average nanoparticle diameters are 49 (2) nm for the sample with 5 % of (NH 4 )H 2 PO 4 (ADP) and 46 (2) nm for the nanocomposites with 15 % of ADP. Dielectric response data analysis have revealed the shifts of the ferroelectric phase transition temperature as a function of (NH 4 )H 2 PO 4 concentration: at x = 0 ∆T C is equal to ∼6 K, at x = 0.05 ∆T C ∼3 K and at x = 0.15 ∆T C ∼2 K.

Phase diagram for K(1-x)(NH4)(x)H2PO4 (x = 0 - 0.15) solid solutions embedded into magnetic glasses

“…The principle feature of all dependences C(T ) is the presence of a shift in the maximum position on cooling and heating. We have observed a similar hysteresis for NCM based on conventional PG [6] with embedded KADP. Temperatures of ferroelectric phase transition (T C ) on cooling and heating have been determined from the maximum positions for every sample, with an accuracy in the determination of T C of better than 0.1 K. In Fig.…”

“…The phase diagram for the bulk KH 2 PO 4 (KDP) and (NH 4 )H 2 PO 4 (ADP) solid solutions (KADP) are known [4,5] and it is shown that a small admixture of ADP leads to a drastic decreasing of the ferroelectric phase transition temperature T C . In previous work [6] we studied the effect of restricted geometry on this phase transition for NCM based on conventional porous glasses (PG) with KADP at low ADP concentrations. It has been revealed that there are the shifts in the ferroelectric phase transition temperature, to higher temperature T C , as a function of ADP concentration on cooling and heating in comparison with the bulk KADP at the same (NH 4 )H 2 PO 4 concentrations.…”

“…So the effect of ADP admixture on T C in confinement becomes less pronounced than in the bulk KADP. The principal goal of the present work was to study the influence of applied magnetic fields on T C for NCM based on magnetic glasses with internal parameters similar to those of nonmagnetic alkali borosilicate glasses in the paper [6].…”

“Restricted Geometry” Effect on Phase Transitions in KDP, ADP, and CDP Nanocrystals

“…An influence of the pore size on the phase transition temperature in KDP and ADP particles, embedded in porous matrices, has already been discussed [8][9][10][11]13]. However, experimental results obtained by different authors contain some contradictions.…”

“…Alongside this, potassium dihydrogen phosphate [8][9][10][11][12][13], Rochelle salt [14,15], and triglycine sulfate [14,[16][17][18][19], in contrast, are characterized by an increase of ferroelectric phase transition temperature under "restricted geometry" conditions. However the data on the magnitude of T C shifting as a function of the matrix mean that the pore diameter varied significantly for different researchers.…”