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Rajeev Ranjan

Publications and source records attributed to Rajeev Ranjan.

46 records · Page 3Linked to original sources
arXiv2015

A Deep Pyramid Deformable Part Model for Face Detection

We present a face detection algorithm based on Deformable Part Models and deep pyramidal features. The proposed method called DP2MFD is able to detect faces of various sizes and poses in unconstrained conditions. It reduces the gap in training and testing of DPM on deep features by adding a normalization layer to the deep convolutional neural network (CNN). Extensive experiments on four publicly available unconstrained face detection datasets show that our method is able to capture the meaningful structure of faces and performs significantly better than many competitive face detection algorithms.

cs.CV↗
arXiv2015

Strong interrelationship between anomalous electric-field induced lattice strain along non-polar direction and domain reorientation in pseudorhombohedral piezoelectric ceramic BiScO3-PbTiO3

The lattice strain and domain switching behaviour was investigated as a function of cyclic field and grain orientation for a pseudorhombohedral composition of the high Curie point piezoelectric system xBiScO3 - (1-x)PbTiO3 (x = 0.40) by in-situ electric field diffraction technique with high energy synchrotron x-rays. Along the field direction, the system exhibts five time large strain along 100 as compared to the 111 direction. A one-to-one correspondence between the 200 lattice strain and the 111 domain switching suggests a strong correlation between the two phenomena.

cond-mat.mtrl-sci↗
arXiv2015

Influence of electric field on the Eu+3 photolumiscence in lead-free ferroelectric Na1/2Bi1/2TiO3

Eu modified Na1/2Bi1/2TiO3 (NBT) was investigated for electric-field induced Eu+3 photoluminescence (PL) and structural changes. Detailed analysis revealed that below a critical Eu composition electric field irreversibly suppresses the structural heterogeneity inherent of the host matrix NBT and brings about a long range ferroelectric state with rhombohedral (R3c) distortion. PL study revealed that structural disorder on the nano-scale opens new channels of radiative transitions which can be suppressed by electric field. This study suggests that Eu+3 luminescence can be used to probe the relative degree of field induced structural ordering in relaxor ferroelectrics and also in high performance piezoelectric alloys where electric field couples very strongly with the lattice and structural degrees of freedom.

cond-mat.mtrl-sci↗
arXiv2015

Crystallite size dependence of morphotropic phase boundary in the multiferroic BiFeO3-PbTiO3

The morphotropic phase boundary (MPB) in the magnetoelectric multiferroic BiFeO3-PbTiO3 is shown to be uniquely dependent on crystallite size. The system exhibits the phenomenon of abnormal grain growth (AGG) during sintering with abrupt increase in the grain size from ~ 1 micron to ~ 10 microns. The large sized free crystallites (10 microns) exhibit pure tetragonal phase. Phase coexistence sets in after reducing the size to ~ 1 micron. These results prove that size, and not the internal stress, as the controlling mechanism for stabilizing phase coexistence in this system.

cond-mat.mtrl-sci↗
arXiv2015

Growth Stress Induced Tunability of Dielectric Constant in Thin Films

It is demonstrated here that growth stress has a substantial effect on the dielectric constant of zirconia thin films. The correct combination of parameters - phase, texture and stress - is shown to yield films with high dielectric constant and best reported equivalent oxide thickness of 0.8 nm. The stress effect on dielectric constant is twofold, firstly, by the effect on phase transitions and secondly by the effect on interatomic distances. We discuss and explain the physical mechanisms involved in the interplay between the stress, phase changes and the dielectric constant in detail.

cond-mat.mtrl-sci↗
arXiv2014

Monoclinic (Mc) phase and electric field induced phase transformation in BaTiO3

For decades it has been a well-known fact that among the few ferroelectric compounds in the perovskite family namely BaTiO3, KNbO3, PbTiO3 Na1/2Bi1/2TiO3 the dielectric and piezoelectric properties of BaTiO3 is considerably higher than the others in polycrystalline form at room temperature. Further, similar to ferroelectric alloys exhibiting morphotropic phase boundary, single crystals of BaTiO3 exhibits anomalously large piezoelectric response when poled away from the direction of spontaneous polarization at room temperature. These anomalous features in BaTiO3 remained unexplained so far from the structural stand point. In this work we have used high resolution synchrotron X-ray powder diffraction, atomic resolution aberration corrected transmission electron microscopy, in conjunction with a novel powder poling technique, to reveal that (i) the equilibrium state of BaTiO3 is characterized by coexistence of a subtle monoclinic (Mc) phase and tetragonal phase, and (ii) strong electric field induces an orthorhombic phase at 300 K. These results suggest that BaTiO3 at room temperature is within an instability regime, and that this instability is therefore the fundamental factor responsible for the anomalous dielectric and piezoelectric properties of BaTiO3 as compared to the other homologous ferroelectric perovskite compounds. The results demonstrate that pure BaTiO3 at room temperature more akin to lead-based ferroelectric alloys close to the morphotropic phase boundary where polarization rotation and field induced ferroelectric-ferroelectric phase transformations play fundamental role in influencing the piezoelectric behavior.

cond-mat.mtrl-sci↗
arXiv2013

Dielectric Investigation, Piezoelectric Measurement and Structural Studies of Strontium-doped, modified PMS-PZT Piezoelectric Ceramics

The structure and dielectric properties of 6% $\rm{Sr}^{2+}$-substituted, modified Lead Zirconium Titanate (PZT) piezoelectric ceramic, with composition $[\rm{Pb}_{0.94}\rm{Sr}_{0.06}][(\rm{Mn}_{1/3}\rm{Sb}_{2/3})_{0.05}(\rm{Zr}_{0.54}\rm{Ti}_{0.46})_{0.95}]O_3$ and lead manganese antimonite as an additional dopant, synthesized by ceramic route have been investigated in a frequency range from 50Hz to 1MHz and in a temperature range between room temperature and 633K. The scanning electron micrograph of the sample taken at the room temperature confirms the formation of a fairly homogenous structure and well-formed grains with sharp boundaries. From the Rietveld analysis, it was found that the structure of the material is tetragonal with space group P4mm. The scaling behavior of imaginary part of the electric modulus suggests that the relaxation is described by the same mechanism at various temperatures. The values of the electromechanical coupling factor ($\rm{k_p}$), the high mechanical quality factor ($\rm{Q_m}$) and the piezoelectric coefficient ($\rm{d}_{33}$) of the synthesized sintered & poled ceramics gives a good set of values for the piezoelectric properties when compared with related materials, useful for various interesting piezoelectric device applications.

cond-mat.mtrl-sci↗
arXiv2006

Anomalous lattice expansion of RuSr2Eu1.5Ce0.5Cu2O10(Ru-1222) magneto superconductor: A low temperature X-ray diffraction study

This is the first report of the observation of the onset of excess volume and also of the strain along the a-axis near the magnetic ordering temperature in Ru-1222 superconductor, and indicates a coupling between the lattice and the magnetism in this system. Magnetization, magneto transport and thermoelectric power measurements being carried out on the same sample are also reported.

cond-mat.supr-con↗
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↗