Low‐Temperature Phase Transition in AgNbO₃

Abstract

AgNbO3 is a weak ferroelectric with antiferroelectricity due to Ag displacements at room temperature. A dielectric anomaly at 250 K, which has not been observed previously, reveals a transition between the weak ferroelectric phase (M1 phase) at the higher temperature and a new ferroelectric phase (M0 phase) at the lower temperature in AgNbO3. This transition was further verified by the pyroelectric current and differential scanning calorimetry measurements. The spontaneous polarization value is found to be much larger in the M0 phase than that of the M1 phase. A well‐defined saturating ferroelectric hysteresis loop can also be observed at 77 K, showing a remnant polarization value of 2.4 μC/cm2 and a coercive field of 25 kV/cm. All the above results indicate that the larger polarization of the M0 phase mainly comes from the alignment of the antiferroelectric displacements of the Ag atoms.

Reply to “Comment on ‘Low‐Temperature Phase Transition in AgNbO3’”

“…Base on the ICP analysis and XRD pattern, the prepared sample is consistent with that reported previously . In our experiments, the prepared powders were ground, pressed into pellets, and then annealed at 1353 K in a flowing O 2 atmosphere for 8 h. To further avoid any contamination of moisture during the dielectric and the DSC measurements, the pellets and the powders were preheated to 473 K with an annealing time of 2 h, and then cooled to room temperature prior to the measurements. As mentioned in our article (Fig.…”

“…Kania and Miga argued that the phase transition occurred in AgNbO 3 around 250 K is connected with the effect of water contamination. We disagree with that the 250 K transition has something to do with water contamination.…”

Comment on: “Low‐Temperature Phase Transition in AgNbO3” J. Am. Cer. Soc., 97 [6] 1895–1898 (2014)

“…in Ref. ) show that below the M 1 –M 2 transition, the low‐frequency dielectric permittivity and losses increase significantly when approaching room temperature. Such behavior was not found for cryostat measurements (Fig.…”

“…4 in Ref. ). In addition, very quick disappearance of losses with frequency increasing indicates that electric conductivity is their main origin, not dielectric process.…”

“…In recent Zhang et al . 's publication, on the basis of dielectric studies and differential scanning calorimetry (DSC) tests, the presence of additional first‐order M 0 –M 1 phase transition in silver niobate AgNbO 3 (AN) at 250 K was postulated. This transition manifests as small maxima (Δε ≈ 5 for 200 Hz) on the background of smooth temperature dependences of dielectric permittivity ε( T ) and huge maxima of tanδ( T ) dependences.…”