Single crystals of DMAAl 1 − x Cr x S were grown using the slow evaporation method from a water solution containing the metal sulfate.
The phase transition temperature T c1 shifts toward lower temperatures when chromium concentration increases to x = 0.2.
DMAAS crystals undergo a second order phase transition of the order-disorder type.
The phase transition temperature T c1 for DMAAS crystals is 152 K.
The temperature T c2 = 110.5 K is considered as a limit of the region of ferroelectric and antiferroelectric phase coexistence.
The presence of chromium affects the parameters of the fundamental ferroelectric dispersion observed around T c1.
A Perkin-Elmer TMA-7 calorimeter was used for DSC measurements.
The substitution of Al ions by Cr enhances thermal stability due to stronger Cr–O bonds compared to Al–O bonds.
The temperature dependence of susceptibility obeys the Curie-Weiss law in both paraelectric and ferroelectric phases.
At higher frequencies, the temperature dependences of ε' show a sharp minimum at Tc1 instead of a peak, and the tangent of dielectric losses tan δ shows maxima at Tc1.
It leads to noticeable changes in the ferroelectric phase transition, thermal decay temperatures, and relaxation time, with critical slowing-down observed at T c1.
The phase transition temperature T c1 for the sample with x = 0.065 was shifted toward higher temperatures by 2.4 K compared to the pure DMAAS.
Isomorphous substitution of metal ions noticeably changes the temperature of phase transition, shifting it toward higher temperatures when chromium is added.
Increasing chromium concentration results in a decrease in the temperature parameter of relaxation time and phase transition temperature T c1, approaching values seen in pure DMAAS crystals.
Chromium ions generate local electric fields that lead to the formation of more massive dipole clusters near the ferroelectric phase transition.
The temperature maximum of ε' in the dispersion region is observed at Tmax = Θ ± ωτ0, indicating the relationship between frequency and phase transition.
The dielectric permittivity ε′ shows sharp anomalies at the temperature T c1 characteristic of the proper ferroelectric phase transition.
The heat capacity measurements indicate that the phase transition has a second order character at any composition.
Chromium ions create stronger Cr-O bonds compared to Al-O bonds, which generate local electric fields that cause reorientation of neighboring dipoles.
The relaxation time τ increases in the vicinity of the phase transition, indicating critical slowing down in the paraelectric phase and speeding up in the ferroelectric phase.
The introduction of Cr3+ causes a considerable shift of the decay temperature toward higher values, especially for samples with lower chromium concentration.
At comparatively low concentrations, chromium ions cause the formation of larger dipole clusters near the ferroelectric phase transition. Higher concentrations lead to fragmentation of these clusters and smaller temperature parameters of relaxation time.
The polar DMA cations execute hindered rotations in the paraelectric phase and order in the spatio-temporal average in the ferroelectric phase.
The dielectric parameters were measured using a traditional method of capacitor capacitance measurement with an automated setup based on an LCR-meter.
At low chromium concentrations, conditions arise that lead to the formation of more massive dipole clusters, while higher concentrations cause fragmentation of these clusters.
The dispersive equation is derived from the Debye equation, relating ε*(ω) to ε' and ε'' through the parameters of the system.
