Shashaank Gupta

Ferroelectric properties and dynamic scaling of ⟨100⟩ oriented (K0.5Na0.5)NbO3 single crystals

In this letter, we report the dielectric and ferroelectric (FE) characteristics of potassium sodium niobate (K0.5Na0.5NbO3) single crystals grown by flux method. Orientation analysis of as-grown cubical-shaped crystals was conducted by electron backscattered diffraction technique revealing the ⟨100⟩ crystallographic orientation of two opposing major faces. Annealed crystals were found to exhibit FE orthorhombic to FE tetragonal transition temperature of 200 °C and Curie temperature of 407 °C. Poled ⟨100⟩ oriented crystals had longitudinal piezoelectric constant of 148 pC/N. Dielectric measurement as a function of temperature was conducted to determine the second order parameter in Gibbs free energy expansion. Dynamic hysteresis analysis on these crystals showed the power law relations to be of the form ⟨A⟩∝f0.47Eo−0.85Eo1.45f0.14 and ⟨A⟩∝f0.04Eo below and above the coercive field.

Fundamental limitation to the magnitude of piezoelectric response of ⟨001⟩pc textured K0.5Na0.5NbO3 ceramic

⟨001⟩pc textured K0.5Na0.5NbO3 (KNN) ceramic was found to exhibit a 65% improvement in the longitudinal piezoelectric response as compared to its random counterpart. Piezoresponse force microscopy study revealed the existence of larger 180° and non-180° domains for textured ceramic as compared to the random ceramic. Improvement in piezoresponse by the development of ⟨001⟩pc texture is discussed in terms of the crystallographic nature of KNN and domain morphology. A comparative analysis performed with a rhombohedral composition suggested that the improvement in longitudinal piezoresponse of polycrystalline ceramics by the development of ⟨001⟩pc texture is determined by the crystal structure.

High thermal stability of piezoelectric properties in (Na0.5Bi0.5TiO3)x–(BaTiO3)y–(Na0.5K0.5NbO3)1−x−y ceramics

We report the piezoelectric and ferroelectric properties of (Na0.5Bi0.5TiO3)x–(BaTiO3)y–(Na0.5K0.5NbO3)1−x−y ceramics for Na0.5K0.5NbO3 rich end of composition (x, y ≤ 0.04 mol. %). These compositions were found to exhibit significantly improved thermal stability of piezoresponse. Variation of dielectric constant as a function of temperature revealed that orthorhombic–tetragonal (To-t) and tetragonal–cubic (Tc) transition temperatures for these compositions were in the vicinity of 0 °C and 330 °C, respectively. Dynamic scaling and temperature dependent X-ray diffraction analysis were conducted. Results are discussed in terms of intrinsic and extrinsic contributions to the piezoelectric response explaining the temperature dependent behavior.

Fatigue mechanism of textured Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics

Grain orientation, BaTiO3 heterogeneous template content, and electrode materials are expected to play an important role in controlling the polarization fatigue behavior of ⟨001⟩ textured Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics. A comparative analysis with randomly oriented ceramics showed that ⟨001⟩ grain orientation/texture exhibits improved fatigue characteristics due to the reduced switching activation energy and high domain mobility. The hypothesis was validated from the systematic characterization of polarization—electric field behavior and domain wall density. The defect accumulation at the grain boundary and clamping effect arising from the presence of BaTiO3 heterogeneous template in the final microstructure was found to be the main cause for polarization degradation in textured ceramic.

Development of KNN-Based Piezoelectric Materials

Piezoelectric materials are technologically important because of their application in various kinds of devices including ultrasonic medical imaging, ultrasonic nondestructive testing, speakers, resonators, gas igniters, gyroscope, pressure sensors etc [1–3]. Piezoelectrics are finding applications in new emerging areas as well such as micromotors, energy harvesting devices, magnetoelectric sensors, and high power transformers [4–6].

Crystal-structure dependent domain-switching behavior in BaTiO3 ceramic

Crystal-structure dependent dynamic scaling behavior was investigated for BaTiO3 ceramic. The scaling relation of the form 〈 〉∝ Af E mn 0 , (where 〈〉 A is the area under the hysteresis loop, while f and E0 represent the frequency and amplitude of the applied electric field signal) was used to determine the values of parameters m and n at various temperatures in the range of �90 °C to 170 °C. The variations in the values of parameters m and n with temperature are explained in terms of the effect of the crystallographic nature of BaTiO3. The values of parameters m and n obtained for the paraelectric regime suggest that the hysteresis in the P–E (polarization–electric field) loops is related to the dielectric loss rather than any domain-related phenomenon.

Local atomic structure of KxNa(1−x)NbO3 by total x-ray diffraction

Local atomic structure of K{sub x}Na{sub (1−x)}NbO{sub 3} with 0.0 ≤ x ≤ 1.0 was studied using atomic Pair Distribution Function analysis based on x-ray diffraction. Powdered crystals were found to exhibit a re-entrant behavior by being orthorhombic (Amm2) for x 0.63. Non-centrosymmetric structure of NaNbO{sub 3} (Amm2) was also evident in the piezoresponse force microscopy analysis revealing the presence of the ferroelectric domains and switching behavior. Lowering of the crystallographic symmetry for 0.42 ≤ x ≤ 0.63 is discussed in terms of differences in the sizes of Na{sup +} and K{sup +} ions and Na–O and K–O bond lengths. Besides being a bridging phase, as suggested by the previous studies on lead-based compositions, present study suggests that lower symmetry monoclinic phase of compositionally disordered perovskite solid solutions could also be a manifestation of the difference in the sizes of constituent ions and bond lengths.

Temperature-time transformation diagram for Pb(Zr,Ti)O3 thin films

In this paper, we describe an analytical model to define the temperature-time- transformation (TTT) diagram of sol-gel deposited Pb(Zr,Ti)O3 thin films on platinized silicon substrates. Texture evolution in film occurred as the pyrolysis and thermal annealing conditions were varied. We demonstrate that the developed model can quantitatively predict the outcome of thermal treatment conditions in terms of texture evolution. Multinomial and multivariate regression techniques were utilized to create the predictor models for TTT data. Further, it was found that multinomial regression can provide better fit as compared to standard regression and multivariate regression. We have generalized this approach so that it can be applied to other thin film deposition techniques and bulk ceramics.

Local atomic structure of K{sub x}Na{sub (1−x)}NbO{sub 3} by total x-ray diffraction

Local atomic structure of K{sub x}Na{sub (1−x)}NbO{sub 3} with 0.0 ≤ x ≤ 1.0 was studied using atomic Pair Distribution Function analysis based on x-ray diffraction. Powdered crystals were found to exhibit a re-entrant behavior by being orthorhombic (Amm2) for x 0.63. Non-centrosymmetric structure of NaNbO{sub 3} (Amm2) was also evident in the piezoresponse force microscopy analysis revealing the presence of the ferroelectric domains and switching behavior. Lowering of the crystallographic symmetry for 0.42 ≤ x ≤ 0.63 is discussed in terms of differences in the sizes of Na{sup +} and K{sup +} ions and Na–O and K–O bond lengths. Besides being a bridging phase, as suggested by the previous studies on lead-based compositions, present study suggests that lower symmetry monoclinic phase of compositionally disordered perovskite solid solutions could also be a manifestation of the difference in the sizes of constituent ions and bond lengths.

Local atomic structure of K x Na (1-x) NbO 3 by total x-ray diffraction

Local atomic structure of K{sub x}Na{sub (1−x)}NbO{sub 3} with 0.0 ≤ x ≤ 1.0 was studied using atomic Pair Distribution Function analysis based on x-ray diffraction. Powdered crystals were found to exhibit a re-entrant behavior by being orthorhombic (Amm2) for x 0.63. Non-centrosymmetric structure of NaNbO{sub 3} (Amm2) was also evident in the piezoresponse force microscopy analysis revealing the presence of the ferroelectric domains and switching behavior. Lowering of the crystallographic symmetry for 0.42 ≤ x ≤ 0.63 is discussed in terms of differences in the sizes of Na{sup +} and K{sup +} ions and Na–O and K–O bond lengths. Besides being a bridging phase, as suggested by the previous studies on lead-based compositions, present study suggests that lower symmetry monoclinic phase of compositionally disordered perovskite solid solutions could also be a manifestation of the difference in the sizes of constituent ions and bond lengths.