Z. Trybuła

Proton glass state in Rb1−x(NH4)xH2AsO4

Abstract A dielectric study of Rb1−x(NH4)xH2AsO4 - RADA mdash; mixed crystals has been made in a wide concentration range x. Both the real and the imaginary part of the dielectric constant were studied in the X-band between 5 K and 300 K and the phase diagram was determined. The proton glass state exists in the concentration range 0.1

Proton glassy state of Rb1−x(NH4)xH2AsO4

Abstract We have presented the first experimental data of the temperature dependence of e′c and e″c for Rb1−x (NH4)x H2AsO4. The results are demonstrated by the presence of a glassy state in Rb1−x (NH4)x H2AsO4 for x = 0.31.

EPR and microwave absorption of alkali metal-doped fullerene superconductors

Abstract Fullerence C60 samples are characterized by a very weak EPR spectrum of g = 2.0025 and linewidth 2ΔB16 ≈ 2 Gs. Like graphite, it is related to the C+60 holes in the defect structure. For fullerence doped with potassium, a strong two-component EPR spectrum was recorded. The narrow line (N) was of width 2ΔBN1s = 2 Gs while the wide line (W) width was 2ΔBW1s = 14 Gs. The fact that the g-value for the narrow line gN = 2.0025 does not change with temperature indicates that it must be determined by an unpaired electron delocalized on the C+60 ion. For the wide line, gW = 2.0017 at room temperature decreases to gW = 2.0006 at the temperature of liquid helium, which suggests that the line originates from Cy−60 anions of KxC60. A strong delocalization of an electron in the complex is indicated by a pronounced temperature dependence of ΔBw1s which at liquid-helium temperature decreases to 2ΔBw1s = 1 Gs. Applying the microwave absorption method, the critical temperature of KxC60 complexes, equal to about 16 K, was determined. EPR spectra of the systems KxMyC60 (M = Li, Cs) are more complex.

Phase transitions in [NH(CH3)3]2MeCl4 (Me = Cd,Zn,Cu) crystals

Abstract Dielectric properties of the new [NH(CH3)3]2ZnCl4 and [NH(CH3)3]2CdCl4 crystals from the [(CH3) n NH4-n ]2MeCl4 group have been investigated in a wide temperature range (4.2–320 K). A series of phase transitions has been discovered at T3 = 325 K,T4 = 251 K,T5 = 193 K, for [NH(CH3)3]2CdCl4 and at T3 = 309 K, T4 = 282 K, T5 = 269 K for [NH(CH3)3]2ZnCl4. A ferroelectric phase has been discovered in the temperature interval T4—T5 from the temperature and frequency dependence of the dielectric permittivity e(T, v). According to optical investigations the existence of ferroelastic phases in the temperature interval T1 = 349 K–T2 = 391 K and below T5 for [NH(CH3)3]2CdCl4 and both above T3 and below T5 for [NH(CH3)3]2ZnCl4 has been ascertained.

Proton glass state in Rb1-x(NH4) xH2AsO4

Abstract Following our previous communication1 about the glass state in Rb0.69(NH4)0.31H2AsO4 system a dielectric study at X-band of the mixed crystals of Rb1-x(NH4)xH2AsO4 was made in a wide concentration range x. Both e′ . and e″ were studied between 5 and 300 K. From dielectric measurements the phase diagram was determined. In the RADA system a proton glass state exists in the concentration range 0.1 < x < 0.5.

Does Highly Dilute KTaO3:Li Undergo Collective Glassy Freezing?

Zero-field heating (ZFH) susceptibility after zero-field cooling (ZFC) and field cooling (FC) of highly diluted single crystalline sample of K0.995Li0.005TaO3, KLT(005) was measured in order to check, if such composition undergoes a collective dipolar glassy freezing. The results are compared with that obtained for the typical glassy system K0.989Li0.011TaO3, KLT(011). It is concluded that the highly dilute KLT(005) compound does not bear convincing features typical of collective dipolar glassy freezing. It is proposed that the low-temperature state of KLT(005) may be considered as a quantum superparaelectric one that may be toggled into an improper ferroelectric while applying an electric field.

Frequency Dependence and Anisotropy of the Glass Transition Tg of Rb0.52(ND4)0.48D2PO4

Abstract The frequency dependence of the glass transition temperature Tg has been calculed from the Vogel-Fulcher law using dielectric data obtained in the 102 Hz to 1010Hz region. The best fit was obtained with 1nfo= 29 and To= 38 K. The anisotropy of Tg predicted recently by theory has been observed.

Anomalies of Dielectric Response in Mixed Ferro-Glass Phase of Potassium Tantalate Doped by Lithium

The measurements of dynamic dielectric response and dc-electric field nonlinear susceptibility in K1−x Li x TaO3 for x = 0.01; 0.016 and 0.03 at 4 ≤ T ≤ 150 K has been performed. It was founded that the field decrease the susceptibility ϵ′ for the two smaller x. For x = 0.03 both the decrease (E > 1 kV/cm) and increase (E < 0.5 kV/cm) of ϵ′ value was revealed. The observed dependence of the position of ϵ′ maxima on temperature and frequency was described by Arrhenius and Vogel–Fulcher law respectively for x = 0.01, 0.016 and x = 0.03. The theoretical description was performed in random field theory framework. The calculations fitted pretty good the experimental data. It was shown that the Arrhenius law is related to the behavior of dipole glass state while Vogel–Fulcher law is the characteristic feature of mixed ferro-glass phase with coexistence of short- and long-range polar order. Therefore the measurements of dielectric response in any disordered ferroelectrics, including relaxors, can be used for identification of ferro-glass phase.

Phase transitions in [Ni(NH3)6](NO3)2

Abstract Electric permittivity e ∗ = e′ − i e″ of nickel-hexammino nitrate (NHN) has been measured within the range of temperature from 9 to 300 K at a frequency of 8.8 GHz (X-band). It has been found that the phase transitions at Tk1 = 247 K and Tk2 = 90 K are discontinuous structural transitions between centrosymmetric phases, whereas the transition at Tc = 63 K is a continuous phase transition (glass?).

Coexistence of the relaxor-like and ferroelectric behavior in K1-xLixTaO3

ABSTRACT The results of low-temperature linear and nonlinear susceptibilities, polarization measurements and the dc electric field dependence of the dielectric properties of the lithium-doped potassium tantalate K1-xLixTaO3, x = 0.034 (KLT-3.4%Li) solid solution are presented. The coexistence of the relaxor-like and ferroelectric behavior and different mechanisms leading to either of them are discussed. The observed ferroelectric phase transition is of the first-order type with temperature hysteresis. This transition is due to the off-center motions of Ta ions in the octahedral environment of oxygen ions. Clusters of Li+ ions produce a relaxor-like behavior and random electric field. This field reduces the depolarization field and allows off-center motions of Ta ions and an appearance of spontaneous polarization.