RESULTS AND DISCUSSION

Thin films of Ba1-xCaxTiO3 with various Ca contents (x and 8 at.%) were successfully synthesized on glass substrate by spray pyrolysis technique. Therefore, the results of these Ba1-xCaxTiO3 thin films will be useful for hard tissue engineering and other various optical optoelectronic applications.

INTRODUCTION

Introduction
Motivation
Objectives of the Present Work
Outline of the Thesis

In the experimental work, spray pyrolysis techniques were used to produce well-crystallized Ba1-xCaxTiO3 thin films. To study the surface morphology of the deposited Ba1-xCaxTiO3 thin films by field emission scanning electron microscopy (FESEM).

LITURATURE REVIEW AND THEORETICALASPECTS

Introduction

A Brief Review of Research Work on Undoped and Ca Doped Barium Titanate Thin Films

The dielectric properties of the prepared samples were measured, revealing that the dielectric permittivity decreased with increasing frequency, and the grain size and Curie temperature of Ba1-xCaxTiO3 ceramics sintered at 1200 °C were greatly affected by Ca substitution. They investigated the effect of mechanical activation of the precursors on the crystallinity and porosity of the material.

Fig. 2.2 FESEM images of samples: (a) BTO fired at 600 °C, (b) BTO fired at 1000 °C [17]

Thin Film

Application of thin films
Different stages of film formation

The formation of thin films depends on the mechanism of condensation between the atoms of the film and substrate. There are three mechanisms of thin film condensation that can be distinguished depending on the strength of interaction between the atoms of the growing film and the substrate.

Fig. 2.7 Applications of Ba 1-x Ca x TiO 3 thin films.

MATERIALSSYNTHESIS AND CHARACTERIZATIONS TECHNIQUES

Introduction

Properties of BTO

Due to the large size of the Ba ions, the octahedral interstitial position in BTO is quite large compared to the size of the Ti ions. There are positions of minimum energy off-center in each of the six oxygen ions surrounding the Ti ion. The structure is notable because two-thirds of the TiO6 octahedra occur in pairs that share a face, forming Ti2O9 coordination groups.

The compensatory deformation occurring in the Ti2O9 groups increases the Ti-Ti distance by 0.33 Å.

Fig. 3.2 Schematic of hexagonal crystal structure of BTO [38].

Precursor Materials

The existence of Ti2O9 groups in hexagonal barium titanate, an unusually stable substance under these circumstances, represents a notable exception to some of Pauling's rules for complex ionic structures [39].

Doping Material

In the spray pyrolysis technique, the structure, composition and other characteristics of the deposited thin layers depend on several deposition parameters. The deposition parameters td, Sr, ds, Pa and C are kept constant when BTO and Ba1-xCaxTiO3 thin films are deposited on glass substrates. Ba1-xCaxTiO3 thin layers are prepared by varying the Ca doping concentration from 2 to 8 at.% at constant Ts values.

The effect of these two film parameters on the structural, optical and electrical properties of BTO and Ba1-xCaxTiO3 thin films is studied in this work.

Deposition Conditions

To select a particular substrate, the lattice parameter of the substrate must be considered to match the lattice parameter of the grown film, otherwise, the structural mismatch may create a mechanical fracture in the film. The temperature of the substrate during film deposition can affect the properties of the film. If the deposition chamber is not evacuated, the vaporized atoms cannot reach the surface of the substrate.

As the deposition rate increases, the film thickness also increases for the same deposition time.

Preparation of Working Solution

Classification of Thin Films Deposition Processes

Spray Pyrolysis Technique

The properties of the thin film will be tailored simply by adjusting or optimizing these conditions to suit a specific application. The deposition rate and thickness of the films can be easily controlled over a wide range by changing the sputtering parameters, thus eliminating the main drawbacks of chemical methods, such as sol-gel, which produces films of limited thickness. By changing the composition of the spray solution during the sputtering process, it can be used to make layered films and films that have composition gradients across the thickness.

Evaporation of the droplets, spreading over the substrate, and drying and decomposition of the precursor salt to initiate film growth.

Fig. 3.3 Schematic representation of spray pyrolysis deposition apparatus.

Thin Film Formation

Fabrication of masks
Air compressor
Heater
The fume chamber
Spray nozzle
Substrate
Substrate cleaning

The mask was placed in close proximity to the substrate, allowing evaporator condensation only in the exposed substrate areas. A regulated power extractor fan is mounted at the top of the chimney to remove unused gases from the room. This partial vacuum causes the liquid to rise through tube 'A' and is expelled by the compressed air in the form of fine spray particles (aerosol).

The cleaning of the substrate has a great influence on the properties of the thin film deposited on them.

Sample Deposition

Characterization Techniques

X-ray diffraction
Field emission scanning electron microscopy
Energy dispersive X-ray spectroscopy
Atomic force microscopy
Thickness measurement of thin film
Optical characterization
Electrical characterization

The surface morphology of the Ba1-xCaxTiO3 thin films was observed by a FESEM using JEOL JSM-7600F at an accelerating voltage of 5 kV. The EDX spectrum is a plot of the intensity of X-rays vs. the energy of the emitted X-ray. The elements of BTO and the incorporation of the Ca element into BTO films were investigated using EDX spectroscopy.

Measurements were made by placing the sample in the impingement beam and another blank glass substrate in the reference beam of the instrument.

Fig. 3.6 A field emission scanning electron microscope set up.

RESULTS AND DISCUSSION

Introduction

A photograph of the as-deposited BTO thin film shows the uniform deposition and surface consistency of the films with Ca doping concentrations. A slight change in depth is observed for Ba1-xCaxTiO3 thin films compared to Ba1-xCaxTiO3 at x = 0.

Chemical Reactions

Surface Morphology

4.2 (b, c), the concentration of oxygen diffusion in the Ba1-xCaxTiO3 ceramic decreases due to the addition of Ca2+ ions, which hinders the growth of the crystal grain and results in the small grain size. When the values of Ca vary from 2 to 4 at.%, the values of the average grain size decreased, and when the values of Ca vary from 6 to 8 at.%, the values of the average grain size of films increased.

Fig. 4.2 FESEM images of Ba 1-x Ca x TiO 3 thin films for various Ca substitution at × 10 k magnification

Elemental Analysis

At x=0, the amounts of Ti and O are lower than Ba in mass percentage in the Ba1-xCaxTiO3 thin films. 4.4 (b-e) small peaks are found for Ca impurities demonstrating the survival of the dopant Ca together with Ba, Ti and O. From this table it can be seen that the at.% and mass% of Ca increase with the increase of Ca concentrations in Ba1-xCaxTiO3 thin films.

It is clear that the crystal grains typically consist of Ba, Ca, Ti and O.

Fig. 4.4 EDX micrographs of Ba 1-x Ca x TiO 3 thin films for various Ca substitution at 350

Structural Analysis

Crystallite size
Strain and dislocation density
Micro-stress
Lattice parameters

The origin of the elongated grains of the deposited Ba1-xCaxTiO3 thin films may be related to the growth of the asymmetric hexagonal phase, if c/a is quite large. For x=0, the crystallite size of the Ba1-xCaxTiO3 film was found to be 189 nm, which increased with the Ca concentration in 2 at.% and then decreased drastically from 4 to 8 at.%. Deformation and dislocation density are very important properties of the crystal structure of the thin films.

The dislocation density is defined as the length of dislocation lines per unit volume of the crystal structure, and is estimated from the following relationship using the formula of Williamson and Smallman [61].

Fig. 4.5 XRD pattern of Ba 1-x Ca x TiO 3 thin films.

Thickness Measurement

The thickness of the Ba1-xCaxTiO3 thin films was measured by the Fizeau fringe method.

Surface Topography Analysis

4.7, the three-dimensional view shows that the growth of film takes place with closely spaced sharp "peaks and valleys" above the substrate in the scanned area of 10.3. The behavior is strongly reflected in the dependence of RMS values on the film thickness. The RMS roughness increased for thicker samples due to the increase of successive grains oriented in different directions relative to the substrate normal [67].

Fig. 4.7 Three dimensional view of AFM images of Ba 1-x Ca x TiO 3 thin films for various Ca substitution

Optical Properties

Transmittance
Absorption coefficient
Refractive index
Extinction coefficient
Optical conductivity
Optical bandgap

The shift in the absorption edge indicates the lowering of the band gap (red shift) of the deposited thin films. Also, η is found to be low for higher doping concentration which may be due to the presence of impurities and defects within the crystal lattice of Ba1-xCaxTiO3 thin films. Extrapolation of the linear part of the plot (αhν) 2 vs E at α=0 is used to obtain the band gap value of the film samples of Ba1-xCaxTiO3 thin films.

From the Tauc plots, the initial increase in the optical band gap is due to the reduction of the grain size of Ba1-xCaxTiO3 thin films with Ca ions up to 4 at.% Ca doping.

Fig. 4.8 Transmittance of Ba 1-x Ca x TiO 3 thin films for various Ca substitution.

Electrical Properties

I-V characteristics
Temperature dependent electrical resistivity
Variation of activation energy

After doping with Ca, the current density of Ba1-xCaxTiO3 thin film is more up to 8 at.% than Ba1-xCaxTiO3 thin film at x=0. The electrical resistance of the thin films was calculated using the I-V graphs at room temperature. The ρ values of Ba1-xCaxTiO3 thin films increase after 2 to 4 at.% doping concentration of Ca and decrease again as the Ca concentration increases from 6 to 8 at.%.

2𝑘𝐵𝑇+ ln 𝜎0 (4.19) To calculate the activation energy, the logarithmic change of electrical conductivity with 1000/T for and 8 at.% Ba1-xCaxTiO3 thin layer was taken, as shown in fig.

CONCLUSIONS

Summary

The measurement of the thickness of the deposited Ba1-xCaxTiO3 thin layers was performed using the Fizeau edge method. The thicknesses of the deposited Ba1-xCaxTiO3 thin layers were measured in the range from 407 to 429 nm. AFM images showed two- and three-dimensional views of the surface topography of Ba1-xCaxTiO3 thin films.

The current density of Ba1-xCaxTiO3 thin films is more up to 8 at.% than Ba1-xCaxTiO3 thin films at x = 0.

Conclusions

From the electrical resistance measurement data, it is shown that the lowest electrical resistance is found for Ba1-xCaxTiO3 thin films at x = 0. It is also observed that the electrical resistance increases with the values from 4.98×103 to 11.95×103 Ωm with increasing from 0 up to 4 at.% Ca doping concentration. Ba1-xCaxTiO3 composite that promotes the rapid regeneration of damaged tissue and cell growth in the biological systems.

These Ba1-xCaxTiO3 thin films can also be used in thermistor, heat sensor and various optoelectronic applications.

Suggestions for Future Work

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91] Hasnat, A., and Podder, J., “Optical and Electrical Characteristics of Pure Cds Thin Films for Different Thicknesses,” J .