Hydrothermal Syntheses and Structural Phase Transitions of AgNbO₃

Abstract

The phase‐pure AgNbO3 has been prepared through the hydrothermal reactions of NH4HF2, Ag2O, and Nb2O5. The room‐temperature powder X‐ray diffraction analysis reveals that it crystallizes in orthorhombic perovskite lattice with a space group of Pmc21 and cell parameters a = 15.6999(9), b = 5.5521(1), and c = 5.5830(1) Å. The temperatures, pH values, and times play crucial roles in obtaining phase‐pure silver niobate. The structural phase transitions were observed at 813 K from cubic to tetrahedral phase and to final orthorhombic phase at 718 K, confirmed by TGA‐DTA.

Low‐Temperature Phase Transition in AgNbO3

“…The AgNbO 3 powders were prepared by the hydrothermal method, as we reported previously. 11 The prepared powders were ground, pressed into pellets, and then annealed at 1353 K in a flowing O 2 atmosphere for 8 h. The X-ray diffraction data for the sintered powder were collected on Rigaku D/Max 2500V/Pc X-ray diffractometer (Tokyo, Japan) with Cuk a radiation (k = 1.5418 A) at 50 kV and 200 mA at room temperature. The morphology of the sintered pellet was checked with a JEOL JMS-6480LV scanning electron microscope (SEM; Tokyo, Japan).…”

“…However, some early reports have shown that the M1 phase has a centro‐symmetric space group Pbcm which does not allow the existence of a spontaneous polarization at room temperature . Later, neutron and synchrotron powder diffractions at room temperature revealed that the M1 phase actually belongs to a non‐centrosymmetric space group Pmc 2 1 . Accordingly, the M1 phase should be ferroelectrically active along the c direction .…”

“…9 Later, neutron and synchrotron powder diffractions at room temperature revealed that the M1 phase actually belongs to a non-centrosymmetric space group Pmc2 1 . 10,11 Accordingly, the M1 phase should be ferroelectrically active along the c direction. 10 Unfortunately, there is only a very small P s value of 0.04-0.09 lC/cm 2 observed in the M1 phase, possibly due to the coexisting of FE and AFE components in the M1 phase.…”

Polarization fluctuations in the perovskite-structured ferroelectric AgNbO3

“…Similar to other perovskite niobates, AgNbO 3 undergoes a complex series of phase transitions as a function of temperature, pressure, and electric field, and many details about the subtly different ferroelectric (FE) and antiferroelectric (AFE) states are still not well understood, prompting a number of experimental and theoretical studies in recent years [2][3][4][5][6][7][8][9][10].…”

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. 3 In our experiments, 2 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.…”