Proton glassy behavior inRb1−x(NH4

Abstract

The mixed crystal Rb & "(NH4)"HzAs04 of ferroelectric RbH&As04 and antiferroelectric NH4HzAs04 has been investigated for several values of x by measuring the dielectric constant along the a and c axis in the temperature range from 30 to 200 K. The phase boundary between the ferroelectric phase and the proton glass state is found to be between 0.13 and 0.20, and a similar boundary between the proton glass state and the antiferroelectric phase is observed to be located between 0.44 and 0.49. For samples with 0.23~x~0.44, the dielectric data can be scaled using the Vogel-Fulcher law with a static freezing temperature To. From our experimental results, we construct a phase diagram of Rb, "(NH4)"H&As04.

Thermodynamics, dielectric permittivity and phase diagrams of the Rb_{1-x}(NH_{4})_{x}H_{2}PO_{4} type proton glasses

“…In Rb 1−x (NH 4 ) x H 2 AsO 4 ε 11 (T, ν) found in [18] (1 kHz) for x = 0.4 (proton glass phase) is about 20% smaller, whereas that found in [17] (10 kHz) for x = 0.44 is about 10% smaller than that measured in [15] Lots of other experimental data are available, which disagree within 10%. Such discrepancies can be explained by errors in measurements of ε 11 (T, ν) and ε 33 (T, ν), as well as by an incorrect determination of x.…”

“…It becomes larger and sharper with lowering x. Such a behavior of ε 33 (T, ν) was observed in [17], and K 1−x (NH 4 ) x H 2 PO 4 [22,23,54,55].…”

“…Thus, T c of Rb 1−x (NH 4 ) x H 2 AsO 4 determined from the maximum of ε 33 (T, ν) in [17] are about 10 K larger than T c determined from the maximum of ε 11 (T, ν) in [16]. This means that the value of x is either overestimated in [17] or underestimated in [16].…”

“…Using the experimental data for transverse dielectric permittivity of [17], and K 1−x (NH 4 ) x H 2 PO 4 [19,22,60] it has been established that ε 11 (T, ν) in antiferroelectric phase composition region at T > T N (x), just like in the glass and ferroelectric phase composition region, increases with lowering temperature, but the value of ε 11 (T, ν) here is somewhat larger. Near T N (x) a fast decrease of ε 11 (T, ν) takes place, which at x → 1 transforms into a break.…”

“…Experimental measurements of the dielectric permittivity of Rb 1−x (NH 4 ) x H 2 PO 4 [1][2][3][4][5][6][7][8], Rb 1−x (ND 4 ) x D 2 PO 4 [7,[9][10][11][12][13][14], Rb 1−x (NH 4 ) x H 2 AsO 4 [15][16][17][18], and K 1−x (NH 4 ) x H 2 PO 4 [19][20][21][22][23] in the glass phase composition region have shown that the temperature curves of the longitudinal ε 33 (T, ν) and transverse ε 11 (T, ν) permittivities are qualitatively similar. At high temperatures the real parts of the permittivities are roughly described by the Curie-Weiss law.…”