Barium titanate is perovskite material as it has relatively high permittivity and the ferroelectric properties that it possesses are excellent too. These play a major role in developing the credibility of the material. These nanoparticles are highly expert in carrying out different applications all of which are extremely useful and play a major role in paving the way for this material to reach the heights of success. Their properties and characteristics are excessively excellent as they manifest their working mechanics through those properties.
The typical perovskite structure material, barium titanate (BaTiO3: BTO), is the most extensively studied ferroelectric ceramic because of its characteristics like ferroelectric and high-permittivity characteristics. Memory applications, high dielectric capacitors, actuators, and transducer are those applications in the electronics industry that depends on spontaneous polarization’s existence in the crystal unit cell. Barium titanate is appropriate for electro-optical devices, multilayer ceramic capacitors, thermistors, sensors, and other universal electronic ceramics. There have been investigations on a thin dielectric layer in the mentioned applications for the purpose of miniaturizing and improving the performance of the dielectric.
The composition of perovskite ceramic's surface, their crystallinity, shape, and size, is what makes them this famous but all of them depends on the physical structure and their process of synthesis. Sol-gel and hydrothermal processes are such wet chemical methods that are typically used for synthesizing nanoparticles (NPs) and there has been a huge amount of studies on them for manufacturing nanoparticles of barium titrate with high purity. A huge amount of attention is being received by the sol-gel method because of the comparatively homogeneity, reliability, and ease in the manufacturing and processing of the nanomaterials with high purity.
Usage of metal alkoxides
As compared to hydrothermal process and solid-state reaction, utilizing metal alkoxides in the sol-gel process as a precursor contains more advantages due to the structure's molecular level control and composition. Although, we attained barium titanate at room temperature during the sol-gel process and it can be converted into crystalline barium titanate through the annealing treatment. However, the particles tend to get agglomerated as a result of the heat treatment, therefore increasing the particle's size.
However, spherical barium titanate with powder of smaller size (less than 1 μm) can be directly manufactured through the conventional hydrothermal method at lower reaction temperature as compared to the sol-gel method. Harsh reaction conditions are needed by it, thus needing expensive and special precursors that can withstand high temperature, pH, and pressure.
Agglomeration of nanoparticles
Wang et al. developed the ambient condition sol (ACS) process recently and it provided a solution regarding the problems mentioned above. Controlling the nanoparticles from getting agglomerated through the heat treatment at a lower temperature is possible but it is for obtaining a uniform size of the particle. There are many benefits of the sol-gel process.
One beneficial technology is the ACS process and it has the benefit of its ability to achieve material's homogeneity and high purity. If you implement metal alkoxides in the sol-gel process as a precursor, it will have way more benefits as compared to the benefits that one can get by implementing metal alkoxides in hydrothermal processing and solid-state reaction because of a structure’s facial adoption and control of composition at the molecular level. ACS process is used for utilizing normally chlorine-based precursors to form barium titanate nanoparticles. 18 was the reported small dielectric constant value in the alkoxides precursor's case.
Having (C4H9)4NOH formula, tetrabutylammonium hydroxide (TBAH), is the chemical compound and has TBAH or TBAOH as the acronym. This species is used as a solution in alcohol or water but as a pure compound, it is not achievable. Commonly, it is used in organic chemistry as a base. In organic solvents, TBAH is more soluble as compared to the more conventional inorganic bases, like NaOH and KOH. Being a strong base, tetrabutylammonium hydroxide is usually utilized for influencing deprotonations and alkylation under phase-transfer conditions.
Various mineral acids can be used to neutralize tetrabutylammonium hydroxide in order to give conjugate base lipophilic salts. Strong acidity and long-chain effect with butyl chains can enhance the stability of the nanoparticles. In an aqueous solution, such nanoparticles can be isolated and redispersed again and again. Full characterization is needed for successful utilization of TBAH in applications in the future as their stability and solubility are closely linked to the system’s pH and double-layered structure.
Distribution and size
Here, a chlorine-free ACS process was used to investigate barium titanate nanoparticle's size distribution and morphology depending on TBAH’s concentration. The preferences in manufacturing barium titanate nanoparticles through the ACS process are titanium chloride and barium chloride precursors because of them being easily handled and their cheap chemical input. However, it is extremely difficult to remove the chlorine ions and the electric characteristics and surface properties of the barium titanate nanoparticles might get influenced by the residual ions.
Titanium alkoxide and barium alkoxide have been alternatively utilized as better substitute precursors to obtain chlorine-free barium titanate nanoparticles. Utilizing them as precursors can enable us to suppress the production of chlorides by controlling the chlorine impurities. Heat treatment temperature was diminished by them and they also avoided damage by the HCl during the production of the barium titanate nanoparticles by modified ACS without the usage of the chloride precursor.
Diameter and strengths
With almost 100 nm of diameter, it is a white nanopowder that is made up of cubic barium titanate particles. The remarkable electric and optical characteristics of this material at the nanoscale make it important for a number of applications. Micro-capacitors, lasers, ceramics, and data storage are among the countless other applications and fields on which there has been extensive research.
The major approaches
Advanced and traditional processing are the two main methods for the general synthesis of the BaTiO3 nanoparticles. Barium carbonate and titania go through solid-state mixing at temperatures of 1200 C and more to obtain BaTiO3 conventionally. Submicron and non-uniform particles are the BaTiO3 powders that are made through this method. There are some disadvantages of the conventional preparation method, some of them being the existence of impurity, inhomogeneity, porosity's inevitable existence, multiple phases, and wide grain size distributions. Combined rapid calcination and the wet-chemical process were used to manufacture spherical, pure, and highly tetragonal BaTiO3 nanopowders in the recent literature after calcination for 2 minutes at 1100 C followed by quenching.
Combination of chemicals
Solid-state mixing and wet chemical processing combine thus making this procedure. The microstructural characteristics and purity largely determine the successful manufacturing of barium titanate nanopowders with remarkable dielectric characteristics. Thus, they didn't utilize the traditional method broadly to synthesize barium titanate for and in advanced applications. When it comes to synthesizing NEDs, the usual usage of nanometer-sized pure powders results in developing many advanced processing routes like the alternative chemical methods.
Hydrothermal synthesis is the best synthesis route for nanocrystalline barium titanate as compared to the sol-gel method and other synthesis routes for nanocrystalline barium titanate. The calcination step is neglected by the hydrothermal synthesis and it also enables the synthesis of comparatively pure products at low temperatures however it is also stated that this suggested process is not cheap. According to the reported results, the characteristics are deteriorated by the intraparticle porosity.
There should be a control of hydrothermal synthesis on reaction conditions like temperature, pH, and concentration. One of the main problems that concern development and research is the economic consideration of nanomaterial's mass production. It looks like that the applied research's next step according to nanoscience's progressive growth should be the reduction in the price of the mass production of these materials. Designing based on scientific fundamentals and trial and error are the two included and important approaches in this regard. In each of the industrial process that produces advanced materials, the final price is determined by the two key parameters that are cost and time
Optimization of time and cost
In economic mass production, the vital issue is the optimization of cost and time. For achieving these aims in the sol-gel process, researchers modified the selection process of the precursors, used the ratio of the optimized precursor, lowered the temperature of the synthesis, and shortened the process's time span. Various sol-gel routes have been used to synthesize BaTiO3. A modified method is present in this research to produce barium titanate nanoparticles considering the scientific basis for the sol-gel technique. There were methods of synthesis and preparation of nanoparticles in the previous work that are now modified and enhanced regarding the optical BaTiO3 nano-thin film preparation. They selected proper ratios and optimized precursors and sol was prepared by using low-temperature 2-step hydrolysis.
Polyol assisted method
If you take a look at the present work and compared it with the polyol assisted method, then it can result in the fact that the polyol approach enables a size control due to the functions of alcohol as a surface capping agent to prevent agglomeration but it is not that much established that it can form complex oxides. Most of the time and mostly, this fact is because of the difficulty of the adjustment of the precipitated oxide's final composition when complex stoichiometries are needed because there is a difference in the hydrolysis behavior of different cations.
In addition, the key parameters in the sol-gel method are the costs and processing time of used materials. For instance, they prepared sol for 90 minutes and they spent 1 hour on its calcination. However, 12 hours is minimally needed for preparing a typical complex oxide by using the polyol method. At 100 C, they carried out FT-IR analysis to detect the functional group's presence. It is possible to detect the mechanism of reaction in the sol-gel process by utilizing this analysis.
O-H stretching vibration is assigned with the characteristic absorption of 3416 cm1 because of the C-H stretching vibration and it ensures water’s existence in the xerogel and advocates for the presence of the –CH3 and –CH2 functional groups. Two peaks at 1567 cm1 and 1702 cm1 refers to the existence of acetate groups bonded to barium atoms. The Ba-Ti-O band has a 1421 cm1 characteristic absorption band according to Vaslijev but it doesn't seem acceptable since Ba-O is mainly ionic according to the Pauling semiempirical method and Ti-O displays a combination of ionic and covalent bonding types. IR band in xerogel for Ba-Ti-O was not attained. Sol-gel products are amorphous because of the sol-gel process's nature and its reactions, thus they require drying and calcination subsequently for producing crystalline products.
Below are the calcined powder’s XRD patterns for 1 hour at 600, 700, 800, and 900 C. According to the XRD pattern, it is confirmed that the cubic BaTiO3 phase (with 6 nm average crystallite size) and barium carbonate were present at 600 8C. There comes a decrease in the barium carbonate’s amount by barium carbonate’s further decomposition at 700 C. BaTiO3’s dominant cubic phase’s presence was indicated by XRD pattern at this temperature with 19 nm of average crystallite size and with barium carbonate’s small amount. Barium carbonate disappeared when the samples were fired at 800 C and the pattern displayed a completely crystallized cubic perovskite structure with 26 nm as the average crystallite size. A cubic barium titanate structure was displayed by the sample that was calcined at 800 C.
Peak intensity increased when the temperature was increased to 900 C. Also, the FWHM (full wide at half-maximum) decreased at 900 C, and thus the average crystallite size increased to 32 nm from 26 nm. Scherrer equation was used to calculate BaTiO3’s average crystallite size and the results are presented. Some figures demonstrate that with an increase of the calcination temperature, the size of the average crystallite increases, and the crystallites are of the size of the nanometer.
This method has many advantages, the major one being manufacturing finer crystals in a shorter time span and at a lower temperature. For instance, pure cubic BaTiO3 is made by Lee and Zhang, Yu and Cui, and Xing through calcination for 2 hours at 800 C, for 2 hours at 900 C, and 4 hours at 800 C, but pure cubic BaTiO3 was made for 1 hour in the present research at 800 C. In conclusion, during pyrolysis or calcination, carbonate compounds are produced but their amount can be reduced by lower amounts of acetic acid and 2-propanol leading to lessening in the temperature and time that is needed for synthesis and calcination.
Also, no modifier like acetylacetone was utilized in this research as it can influence the calcination's temperature and time. BaTiO3 is made according to particular reactions after barium carbonate's decomposition and its reaction with TiO2.
Synthesis of the product
Here, the synthesis of tetragonal barium titanate nanoparticles took place at a lower temperature. Peak splitting took place around 2u = 458 because of the tetragonal phase when xerogel was fired for 1 hour at 900 8C. Peak splitting amount increased when they started firing xerogels at 1000-1100 C or higher temperatures, which referred to the fact that there is an increase in polymorphic transformation’s degree. Here, the polymorphic transformation started at a lower temperature as compared to the sol-gel routes that were previously used.
Most significant advantage
One of the significant benefits of this enhanced method is this fact. For instance, tetragonal BaTiO3 was manufactured by Harizanov and Xing for 2 hours at 900.8 C and 1 hour at 1000.8 C by calcination, respectively whereas it could not be made by Lee and Zhang even after it has been fired to 1100.8 C. The SEM micrographs are obtained after calcination of the powders at 800.8 C.
Numerous processes that occur during gel precursor's drying cause high agglomeration of the powders primarily. Also, the small particles that are implanted in each of the agglomerated clusters resemble barium titanate particles in regards to the prepared powder’s size distribution and morphological characteristics. Regularly shaped near-spherical particles consist of this product with a narrow size distribution.
At nanoparticle scales, barium titanate displays many of the research's intriguing avenues that involve the remarkable traits of the barium titanate. Assorted electro-optic devices, dielectric amplifiers, varistors, pyroelectric sensors, micro-capacitors, and piezoelectric devices are the included applications.
- Data storage
The material, barium titanate possesses an extremely high potential for high-density optical data storage just like many nanomaterials that possesses remarkable electric and optical characteristics.
Barium titanate nanopowder is used by various ceramic composites because of its remarkable characteristics like numerous semiconductive ceramics and ferroelectric ceramics. Barium titanate has a lot of potential for manufacturing ceramic capacitors.
- Dynamic holography
Barium titanate particles are best to manufacture particular lasers and mirrors because of their remarkable characteristics. Barium titanate is significant for manufacturing dynamic holography's practical applications in the future.
Optical image processing, pattern recognition, on-chip programming, and optical computing are some of the many exciting cutting-edge computing applications that are offered by these nanoparticles to themselves.
Barium titanate has 7,000 and higher dielectric constant value and it is a dielectric ceramic that is utilized in capacitors. Values like 15000 are possible of the dielectric constant over a narrow temperature range. Usually, a dielectric constant of less than 10 is displayed by the most common polymer and ceramic materials, whereas others like titanium dioxide (TiO2) have values between 20-70.
It is utilized in other transducers and microphones as it is a piezoelectric material. According to earlier studies, at room temperature, barium titanate single crystal’s spontaneous polarization is 0.15 C/m2, whereas, in the recent studies, it is 0.26 C/m2 so it ranges between 0.15 C/m2 and 0.26 C/m2 and its Curie temperature is between 120-130 °C. The differences are related to the growth technique, where the flux-grown crystals were less pure as compared to the crystals that were grown using the Czochralski process,thus having a higher Curie temperature and larger spontaneous polarization.
PZT also called lead zirconate titanate has replaced it on a larger scale as a piezoelectric material. A positive temperature coefficient of resistance is possessed by the polycrystalline barium titanate, resulting in it being a beneficial material for self-regulating electric heating systems and thermistors.
There is the usage of the barium titanate crystals in nonlinear optics as the material can be operated at near-infrared and visible wavelengths and has a high beam-coupling gain. Material’s highest reflectivity is possessed by it and utilized for the applications of self-pumped phase conjugation (SPPC). With its optical power in the milliwatt range, it can be utilized for the purpose of continuous-wave four-wave mixing. Various elements like iron can be used to dope barium titanate for numerous photorefractive applications.
Electrooptic modulation is displayed by barium titanate’s thin films but only to more than 40 GHz frequencies. Barium titanate’s ferroelectric and pyroelectric characteristics are utilized for the thermal cameras in some uncooled sensors’ types.
New barium titanate capacitor energy storage systems have a key component, which according to the reports is the barium titanate powder of high purity and it is for being utilized in electric vehicles.
BTNPs (Barium titanate nanoparticles) are also used as nanocarriers to deliver drugs because of their raised biocompatibility.
In thin films that are grown on the substrates of barium titanate, there have been reports on the magnetoelectric effect of giant strengths.
A major portion of the applications of barium titanate nanoparticles are in the field of electronics and are serving as one of the best products to be found in the industry. All the researches that have been carried out in this regard have been a witness of the credibility and authenticity that this product holds. Hence, barium titanate nanoparticles are extremely useful particles that are providing the industries with the best of favors.