arXiv subjects

Akhilesh Kumar Singh

Publications and source records attributed to Akhilesh Kumar Singh.

23 records · Page 2Linked to original sources

arXiv2008

High-resolution synchrotron XRD study of Zr-rich compositions of Pb(Zr_xTi_1-x)O_3 (0.525\leq x \leq 0.60): evidence for the absence of the rhombohedral phase

Results of Rietveld analysis of the synchrotron XRD data on Pb(Zr_xTi_1-x)O_3 (PZT) for 0.525\leqx\leq0.60 are presented to show the absence of rhombohedral phase on the Zr-rich side of the morphotropic phase boundary (MPB). Our results reveal that the structure of PZT is monoclinic in the Cm space group for 0.525\leq x\leq 0.60. The nature of the monoclinic distortion changes from pseudo-tetragonal for 0.525\leqx\leq0.54 to pseudo-rhombohedral for x>0.54.

cond-mat.mtrl-sci↗

arXiv2007

Dielectric Relaxation and Phase Transition at Cryogenic Temperatures in 0.65[Pb(Ni_1/3Nb_2/3)O_3]-0.35PbTiO_3 Ceramics

Dielectric measurements on 0.65[Pb(Ni_1/3Nb_2/3)O_3]-0.35PbTiO_3 ceramic in the temperature range 90K to 470K shows a relaxor ferroelectric transition around 350K with a Vogel-Fulcher freezing temperature of 338K and appearance of a non-ergodic relaxor ferroelectric phase of tetragonal structure at room temperature. This non-ergodic phase reenters into the relaxor state at low temperatures as evidenced by the appearance of a frequency dependent anomaly in the imaginary part of the dielectric constant around 160K, similar to those reported in other relaxor ferroelectric based morphotropic phase boundary ceramics. The polarization relaxation time for the 160K anomaly also follows Vogel-Fulcher type temperature dependence. Temperature dependent magnetization measurements show that this low temperature anomaly is not linked with any magnetic transition. Elastic modulus and low temperature x-ray diffraction (XRD) measurements reveal a tetragonal to monoclinic phase transition around 225K. It is argued that the low temperature dielectric dispersion around 160K results from the freezing of mesoscopic conformally miniaturized monoclinic domains formed inside the parent tetragonal domains below the structural phase transition temperature of 225K.

cond-mat.mtrl-sci↗

arXiv2004

Barrier layer formation and PTCR effect in (1-x) Pb(Fe1/2Nb1/2)O3]-xPbTiO3 (x = 0.13) ceramics

(1-x)Pb(Fe1/2Nb1/2)O3-PbTiO3(PFN-xPT)Ceramics with x = 0.13 sintered at 1473K show diffuse phase transition and very high dielectric constant at lower frequencies.The high value of dielectric constant at lower frequencies is shown to be due to the barrier layer formation.The resistivity of the PFN-xPT ceramics, obtained by complex impedance analysis, initially decreases with temperature and then shows an upward trend beyond the ferroelectric Curie point reminiscent of BaTiO3 based thermistors with PTCR effect.

cond-mat.mtrl-sci↗

arXiv2004

A Comparison of the Cc and R3c Space Groups for the Superlattice Phase of Pb(Zr0.52Ti0.48)O3

Recent controversy about the space group of the low temperature superlattice phase of Pb(Zr0.52Ti0.48)O3 is settled. It is shown that the R3c space group for the superlattice phase cannot correctly account for the peak positions of the superlattice reflections present in the neutron diffraction patterns. The correct space group is reconfirmed to be Cc. A comparison of the atomic coordinates of Cc and Cm space groups is also presented to show that in the absence of superlattice reflections, as is the case with XRD data, one would land up in the Cm space group. This superlattice phase is found to coexist with another monoclinic phase of Cm space group.

cond-mat.mtrl-sci↗

arXiv2002

Evidence for $M_B$ and $M_C$ phases in the morphotropic phase boundary region of $(1-x)[Pb(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$ : A Rietveld study

We present here the results of the room temperature dielectric constant measurements and Rietveld analysis of the powder x-ray diffraction data on $(1-x)[Pb(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$(PMN-$x$PT) in the composition range $0.20 \leq x \leq 0.45$ to show that the morphotropic phase boundary (MPB) region contains two monoclinic phases with space groups Cm (or $M_B$ type) and Pm (or $M_C$ type) stable in the composition ranges $0.27 \leq x \leq 0.30$ and $0.31 \leq x \leq 0.34$, respectively. The structure of PMN-$x$PT in the composition ranges $0 \leq x \leq$ 0.26, and $0.35 \leq x \leq1$ is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt & Cohen's theory.

cond-mat.mtrl-sci↗