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Ca2+ substituted barium niobate i.e. CaxBa1-xNb2O6 (x = 0.3) compound in nanoparticles form was synthesized by a simple co-precipitation method for the first time and its structural characterization has been done by using powder X-ray diffraction data. Other characterizations were done by using transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. It was found that the CaxBa1-xNb2O6 (x = 0.3) compound stabilizes in the orthorhombic phase (Pbcn space group) with the lattice parameters a = 14.984 A, b = 5.761 A and c = 5.216 A. A representative TEM image shows the irregular sphere like morphology of the synthesized particles with the size ranging from 70 to 120 nm. The optical band gap energy was found to be 3.74 eV. It was observed that the synthesized nanoparticles exhibit excellent H2 evolution tendency and self–activated photoluminescence under the excitation of UV light. These activities were assigned to the nanocrystalline nature of the synthesized material.

Ca0.5Sr0.5Nb2O6 (CSN), a novel compound with crystal structure similar to the well-known orthorhombic columbite compound CaNb2O6 (CN) of alkaline earth niobates family was synthesized by a simple co-precipitation technique. The synthesized material was characterized by using X-ray diffraction (XRD) technique, transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectroscopy, FTIR spectroscopy, and photoluminescence emission spectroscopy. It was found that the CSN compound stabilizes in P b c n space group with the improved symmetry as compared to the CN. The lattice parameters of CSN were found to be comparable with those of CN, and they are: a = 15.013 A, b = 5.757 A and c = 5.198 A. The morphology of CSN and CN particles synthesized by a similar method was found to be identical. However, in CSN stronger self activated luminescence than that of CN was observed. The self-activated luminescence property of CSN was assigned to the niobate octahedral group [NbO6]7− similar to the CN.

Ferroelectric domains in Sr0.5Ba0.5Nb2O6 (SBN50) at nanolevel have been investigated by means of temperature dependence of dielectric permittivity, hysteresis study and the transmission electron microscopy (TEM). The temperature dependence of dielectric constants of SBN50 measured at 100Hz confirmed a ‘relaxor’ nature of the material. The Curie temperature range was found to be shifted towards the room temperature side. Spontaneous polarization values, obtained from the hysteresis loop, were found to be very small. The discrepancy in the observed behavior from the literature reported one was interpreted and correlated to the domain formation in SBN50 nanoparticles. Physical evidences of domain like structures in SBN50 nanoparticles were also reported.

In this paper, we report the existence of polymorphic tetragonal phase in BaNb2O6 (BN) nanoparticles for the first time. Polymorphic tetragonal tungsten bronze (TTB)-like and orthorhombic phases of BN compound were obtained by a citrate-gel method. The obtained TTB-like phase was not solely confirmed by means of X-ray diffraction (XRD) pattern because of the admixture of two phases. However, by the additional characterizations such as morphology of the synthesized particles, well-defined ferroelectric hysteresis loops, and presence of 180° domains the TTB-like phase was identified.

Nanodomains in BaTiO3 nanoparticles were studied by transmission electron microscopy (TEM). Both, 90° and 180° nanodomains were clearly observed under the TEM. The geometries of both types of domains support the pseudo cubic (100) plane as an observed plane and vice versa. Two set of 90° domains, the laminar and the wedge shaped domains were nucleated at grain boundaries and dislocations. The pinning of the 180° nanodomain by 90° nanodomain was also observed. These findings provide useful information for understanding the domain morphology, which can be applicable to other systems.

Some aspects regarding the domain study in ferroelectric nanoparticles by using transmission electron microscopy (TEM) based on the experimental observations of BaTiO 3 and PbTiO 3 nanodomains have been discussed. Experimental observations were found to be consistent with the theoretical aspects.

Ca0.5Sr0.5Nb2O6 (CSN), a novel compound with crystal structure similar to the well-known orthorhombic columbite compound CaNb2O6 (CN) of alkaline earth niobates family was synthesized by a simple co-precipitation technique. The synthesized material was characterized by using X-ray diffraction (XRD) technique, transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectroscopy, FTIR spectroscopy, and photoluminescence emission spectroscopy. It was found that the CSN compound stabilizes in P b c n space group with the improved symmetry as compared to the CN. The lattice parameters of CSN were found to be comparable with those of CN, and they are: a = 15.013 A, b = 5.757 A and c = 5.198 A. The morphology of CSN and CN particles synthesized by a similar method was found to be identical. However, in CSN stronger self activated luminescence than that of CN was observed. The self-activated luminescence property of CSN was assigned to the niobate octahedral group [NbO6]7− similar to the CN.