lead - free materials are of interest as new candidates to interchange the widely used lead - based ceramics owing to their pollution free environmental friendly character throughout the preparation process . materials that can absorb microwaves will eliminate electromagnetic radiation pollution .
wide unfolding applications of electromagnetic absorbers have affected engineers to explore relating to optimum design without their algorithms .
the dielectric , electric , acoustic , mechanical , temperature , magnetic , and optical properties of these materials are used in a wide number of electronic applications .
components based on ferroelectric phase have a wide range of commercial applications like memory cells sensors , actuators , and so forth .
perovskites are excellent dielectrics characterized by extraordinarily high dielectric permittivity that rely on the ferroelectric technology for microwave applications are creating their way to the industry and commercial applications , like wireless sensor networks , safety and security systems , automotive , medical , environmental food monitoring , radio tags , and so forth .
good dielectrics and electric field dependent permittivity make the parametric phase ferroelectrics attractive for the development of a wide range of tunable microwave devices for applications in agile microwave systems .
the materials ' property from engineer 's perspective , device , and system ( circuit ) applications of the ferroelectrics plays very important role .
recent dramatic changes in microelectronics and in particular wireless communications technologies have made the importance of materials with the unusual combination of high dielectric constant , less dielectric loss , and low temperature dependence of dielectric constant of great interest .
relaxor ferroelectrics exhibit a high - dielectric constant over a wide temperature range around the ferroelectric phase transition .
ferroelectric srxba1xnb2o6 ( 0.25  x  0.75 ) with the ttb ( tetragonal tungsten bronze ) structure has attracted a great deal of attention and is being investigated as a potential material for pyroelectric , electro - optic , and photorefractive devices [ 3 , 4 ] . recently , it was reported that the hexagonal phase of banb2o6 transforms above 1200c to the orthorhombic structure .
these microwave dielectrics can be synthesized by several roots syntheses like chemical methods , the coprecipitation , sol - gel , and hydrothermal and colloid emulsion techniques [ 59 ] .
the purpose of this study was to prepare banb2o6 ceramics using simple low cost solid state technique from simple inorganic materials .
a detailed significant investigation of the structural , microstructural , and mechanical properties of barium niobate has been reported .
electromagnetic transmittance and absorption of samples in the x band frequency range frequencies using waveguide reflectometer technique are reported .
ar grade chemicals of high purity barium carbonate ( baco3 ( 99.95% ) ) and niobium penta - oxide ( nb2o5 ( 99.999% ) ) were used as starting materials .
this powder was again mixed in stoichiometric proportion and ground for 4 hours in acetone medium to obtain the desired compound .
this mixture was initially sintered at 1200c for 10  hrs and further at 1000c for 24 hours in a muffle furnace ( given by ( 2 ) .
the flowchart of barium niobate ( banb2o6 ) ceramic is shown in figure 1 : 
 ( 1)baco3+nb2o5banb2o6+co2 
 the phase analysis was confirmed by x - ray diffraction using cr - k radiations ( philips diffract meter pw 3710 ) . the structural parameters such as the lattice constants , average crystallite size , and texture coefficients
this powder was pressed into pellets in a hydraulic press at 10  ton / cm for 10 minutes .
the surface morphology was studied using scanning electron microscope ( sem jeol - jsm 6360 ) .
transmission of microwaves due to bulk sample was measured point by point using transmission / reflection method with rectangular waveguide , consisting of the x band generator , isolator , attenuator , directional coupler , and rf detector .
x - ray diffraction technique is a powerful tool to analyze the crystalline nature of the materials . if the material to be investigated is crystalline , well defined peaks will be observed .
x - ray diffractogram of barium niobate 2 values from 20 to 90 is shown in figure 2 .
the barium niobate has tetragonal structure with lattice parameters a = b = 12.34   and c = 3.89   ( table 1 ) .
nanocrystalline ( particle size ) characteristics of the samples depend on the broadening of the xrd lines .
average particle size of the calcined powder was 37.5  nm , determined using debye - scherer formula : 
 ( 2)d = kcos , 
 where k is scherrer constant ( k = 0.9 ) ,  is bragg 's angle , and  is full - width half maxima ( fwhm ) in radians .
dislocations are 1d crystalline defects marking the boundary between slipped and unslipped regions of material .
the amount of defects in the as - deposited film is assessed by dislocation density ( d ) .
it is defined as the deformation of an object divided by its effective - length . the dislocation density
( d ) and microstrain (  ) were calculated as 
 ( 3)dislocation  densityd=1d2,(4)=cos4 . 

the williamson - hall equation is used to calculate the strain (  ) and particle size of the sample graphically given by [ 11 , 12 ] 
 ( 5)cos=0.9d+4sin , 
 where  is the lattice microstrain , d is the grain size ( in  ) ,  is the wavelength of the radiation ( in  ) ,  is the bragg angle , and  is full - width half maxima ( fwhm ) of a xrd peak in degree . using a linear extrapolation fit to williamson - hall analysis plot ( shown in figure 3 ) , the intercept gives the particle size ( d ) and the slope represents the strain (  ) .
microstrain (  ) , crystallite size ( nm ) , and dislocation density ( d ) are tabulated in table 2 .
texture is perceived in almost all engineered materials which can have a great influence on properties of materials .
diffraction patterns from samples containing a random orientation of crystallites have predictable relative peak intensities .
texture frequently represents a pole figure , in which a defined axis ( crystallographic ) from each of a representative number of crystallites is mapped in a stereographic projection .
quantitative data concerning the preferential crystal orientation can be obtained from the texture coefficient ( tc ) : 
 ( 6)tchkl = ihkl / i0hkl1/nnihkl / i0hkl
. if the crystallographic orientations are fully random , then the sample has no texture .
if the orientations are not random but have some preferred orientation , then the samples have a weak , moderate , or strong texture . as tc(hkl ) increases , the preferential growth of the crystallites in the direction perpendicular to the hkl plane is greater ( table 3 ) . from the texture analysis preferential grain growth which is observed at ( 210 )
plane is more dominant ( tc = 2.977 ) and that observed at ( 311 ) plane is weak .
the morphology of barium niobate ( banb2o6 ) is like typical pebble ( beach stone ) structure ( shown in figure 4 ) .
the image shows homogenous grains distributed over the entire volume of the samples and shows good crystallization .
it is clear from the micrographs that the grains are densely packed in the sintered sample .
however , a certain degree of porosity is still observed . the shape and distribution of grains in the microstructure exhibit the polycrystalline nature of the sample .
the grain size of the sample ( obtained from sem ) is larger than of the crystallite size obtained from scherrer 's equation .
the advantages of solid - state reaction are simplicity and low cost , but the disadvantages are that the high calcining temperature results in very large grain sizes confirmed by sem images . the infrared spectral analysis is effectively used to understand the chemical bonding and it provides information about molecular structure of the synthesized compound .
the characteristic absorption peaks in the range from 400 to 4000  cm are shown in figure 5 . using perkin elmer spectrophotometer , fourier
transform infrared ( ftir ) spectra of sample ( in pellet form mixed with kbr ) were recorded in the range 4004000  cm .
the sharp absorption peaks at ~3470  cm indicating the presence of hydroxide group ( oh ) result from surface - adsorbed atmosphere ( like moisture and humidity ) .
the strong absorption bands at ~816  cm , 641  cm , and 482  cm are associated with the coupling mode between nb  o stretching modes .
the insertion loss ( transmission ) and absorption loss of barium niobate sample were measured by the rectangular waveguide reflectometer setup shown in figure 6 .
the microwaves were incident on the device under test ( dut ) in the frequency range 8  ghz to 12  ghz ( x band ) .
the waveguide reflectometer setup consists of gunn oscillator , isolator , attenuator , two 3  db directional couplers connected in reverse directions , sample holder for device under test ( dut ) , and the diode detector .
the system was calibrated by measuring the output with and without the dut [ 4 , 17 ] .
the variation of insertion loss and absorption loss of barium niobate is a function of frequency in the x band ( 812  ghz ) which exhibits trivial wavy like nature shown in figure 7 .
the average absorbance is relatively more compared to transmittance . at 9.8  ghz frequency , dip absorbance ( 53  db ) may be the motion of active ferroelectric nbnb also because the frequency of the hopping ions could not follow the applied field frequency and it lags behind .
absorption is the heat loss under the action between electric dipole or magnetic dipole in material and the electromagnetic field .
these barium niobates may be used to function as sensors , actuators , detectors , filters , resonators , and so forth through special layout arrangements .
lead - free ferroelectric barium niobate that has been synthesized by the solid state reaction method was investigated .
it absolutely was shown by x - ray diffraction that the space temperature shows tetragonal structure , lattice parameters a = b = 12.343   and c = 3.889   , and average particle size was 37.5  nm with preferred ( 210 ) textured orientation .
pebble ( beach stone ) like morphology with grain size varied within the range of 24  m , confirmed by sem .
the robust absorption bands at ~816  cm , 641  cm , and 482  cm are related to the coupling mode between nb  o stretching modes .
microwave studies ( absorbance and reflectance ) depict periodical behaviour which can be used to perform like sensors , actuators , detectors , and filters .
 the structural and microwave studies of lead - free barium niobates ceramics prepared by the high temperatures solid state reaction technique are reported . the structural parameters such as the lattice constants , average crystallite size ( d ) , texture coefficients ( tc ) , dislocation density , and microstrain 
 have been determined using x - ray diffraction data . 
 surface morphological studies were carried out using scanning electron microscopy ( sem ) technique . 
 the strong absorption bands at ~816  cm1 , 641  cm1 , and 482  cm1 are associated with the coupling mode between nb  o stretching modes observed in ftir studies . 
 the electromagnetic transmittance , absorption , studies of barium niobates in the x band frequency range frequencies using waveguide reflectometer technique are reported . 
1. Introduction
2. Materials and Methods
3. Conclusions