Phase stability of ferroelectric KNO3 switching devices during polarization aging

Abstract

The persistent observation of polarization aging during repeated room-temperature switching of metastable thin-film ferroelectric potassium nitrate capacitors has led to the conjecture that the observed polarization decay is a direct consequence of a concomitant phase III to phase II structural transformation. Appropriate large area thin-film devices have been fabricated to perform this x-ray diffraction study of the phase stability of ferroelectric KNO3 devices during in situ electrical switching. As the initial remanent polarization of 7.5 μC/cm2 decreases to <0.4 μC/cm2 in <2×106 polarization reversals, the volume fraction of III-KNO3 remains constant, and no reflections from II-KNO3 appear. After complete polarization loss, however, the initial d spacings measured for III-KNO3 have increased an average 0.4%. Examination of the line shapes during aging reveals that the observed shift is not a continuous transition, but a convolution of reflections centered at the initial and final d spacings. This characteristic modification to the original cell, here designated III′-KNO3, occurs throughout the switched volume. The simultaneous loss of polarization and appearance of the expanded unit cell suggest that III′-KNO3 either pins the polarization or is itself nonferroelectric.

Experimental studies for stability of ferroelectric phase in potassium nitrate composite films

“…The diffraction peaks of KNO 3 at 2θ = 29.85°of (003) reflection for ferroelectric phase III and 2θ = 29.2° of (012) reflection for phase II have already been reported in literature [30, 31]. These reflections have also been observed in the X‐ray diffraction scan of the 50 wt% composite film as shown in Fig.…”

“…4a. X‐ray diffraction measurements have been done by various researchers [27, 30, 32] to know the crystal structure and values of different phases of KNO 3 .…”

Preparation and Characterization of the Ferroelectric Potassium Nitrate: Poly(vinyl alcohol) Composite Films

“…The most common diffraction peaks of phase II at 2θ = 23.57°, 23.83°, 29.40°, 32.33°, and 32.82° were observed in the Kno 3 powder for the planes of (h k l) values (111), (021), (012), (102), and (112), respectively. These peaks have also been seen in the Xrd patterns of Kno 3 taken by schaffer and Mikkola [41]. The lattice parameters a, b, and c for Kno 3 have been calculated from Xrd pattern for pure Kno 3 and were found to be 6.552, 5.472, and 9.028 Å, respectively.…”

“…It has been reported that the preparation of the composite films of nano 2 , selenide with PVa using solvent cast technique was helpful in controlling the growth of nano 2 , and selenide nanoparticles [10], [22]. Many studies using techniques such as far infrared [25], neutron diffraction [26], inelastic neutron scattering [27], raman spectroscopy [28], [29], X-ray [30]- [32], differential scanning calorimetric [33]- [35], dielectric [36], electrical and thermal conductivity [36], [37], and ferroelectric [38]- [41], have been carried out in the past by various researchers to examine the nature of the phase transitions in Kno 3 . The technological interest in Kno 3 thin films originates due to the reason that these films have low operating voltage and fast switching response.…”

Ferroelectric Properties of Polyvinyl Alcohol: Potassium Nitrate Composite Films

“…It exhibits ferroelectric behaviour in phase III. KNO 3 has been found to be ferroelectric in bulk form [7] and in thin fused layers [8] quenched to room temperature.…”