Dielectric and Impedance Spectroscopic Investigation of (3-Nitrophenol) -2,4,6-Triamino-1,3,5- Triazine: An Organic Crystalline Material

Department of Physics, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences, andalam, Chennai 602 105, India Department of Physics, Indira Institute of Engineering and Technology, V.G.R. Nagar, Pandur, iruvallur 631 203, India Department of Physics, Rajalakshmi Institute of Technology, Kuthambakkam, Chennai 600 124, India Department of Physics, College of Natural and Computational Science, Wollega University, Nekemte, Ethiopia


Introduction
Single crystals with low dielectric constant, high electro-optic coe cient and ideal reaction rate, and signi cant thermal stability play a crucial role in producing e cient crystalline materials that might be used in optical data storage, communication, and optoelectronic systems [1][2][3][4][5]. Dielectric spectroscopic studies will be used to determine the electric eld distribution in the formed crystal. e frequency and temperature-dependent dielectric characteristics of the produced material reveal the 3NPTAT single crystal's applicability for a variety of applications. e dielectric characteristics of formed crystals were investigated at frequencies ranging from 50 Hz to 5 MHz. e dielectric behavior of a substance is based on its electrical properties. Materials with a high dielectric constant and low dielectric losses are said to be more suitable for electronic applications. e permittivity of nonconductive materials was previously measured using a dielectric spectroscopic approach [6][7][8][9][10][11]. Dielectric characteristics also provide useful information regarding materials and design parameters for a variety of applications. Complex impedance spectroscopic examination of frequency-dependent electrical and dielectric properties of materials provides signi cant information about their electrical microstructure [12][13][14]. e e ect of solvent on material properties using impedance has been discussed by S. Khera and P. Chand in their investigation of ZnO [15]. e complex characteristics such asdielectricpermittivity, electrical modulus, impedance, and admittance in the complex plane were shown to explain the whole electrical topography of material by creating a graph between real and imaginary parts in the dielectric spectrum. Dielectric spectroscopic investigations of organic single crystals with desired NLO properties have already been reported by many researchers [16][17][18][19][20]. e dielectric and impedance behavior of 3-nitrophenol -2,4,6-tri amino-1,3,5-triazine (3NPTAT) is investigated in this study as a continuation of our research effort in organic NLO materials. We discovered that 3NPTAT has considerable optical transparency throughout the visible spectrum, implying that the dielectric susceptibility is related to precise ordering in the dielectric dipole density. To demonstrate the effect of grain and grain boundaries on the electrical properties of a produced material, we used a combined analysis of modulus and impedance spectroscopy investigation. e authors planned the study to include dielectric measurements as well as conductivity and impedance measurements on the formed crystal.

Experimental
e slow evaporation approach was used to make a single crystal of 3-nitrophenol -2,4,6-tri amino-1,3,5-triazine (3NPTAT) using an equimolar ratio of melamine and 3nitrophenol. Melamine was dissolved in distilled water and gently heated before adding an aqueous solution of 3nitrophenol to the hot melamine solution. e mixture was then thoroughly agitated for 6 hours at 70°C to obtain a homogeneous solution. To obtain the purity of the salt, a recrystallization process was carried out. Tiny and transparent single crystals of 3NPTAT were produced for 25-30 days [21]. e schematic of the synthesis procedure is given in the flow chart in Figure 1, and the growth mechanism of the 3NPTAT single crystal is shown in Figure 2.
e dielectric characterization of the synthesized compound is carried out using a suitably cut and polished pellet made of 3NPTATcrystal. Dielectric studies of 3NPTATcrystal were performed at different temperatures and frequencies in the range of 313 K-373 K and 50 Hz-5 MHz, respectively, using the HIOKI model 3532-50 LCR HITESTER impedance analyzer. e polished sides of the crystal pellet have been coated with silver paste and air-dried (for good ohmic contact) to make parallel electrodes.

Results and Discussion
3.1. Dielectric Analysis. Permittivity ε * , conductivity σ * (x), and permeability μ * (x) are inherent electrical properties of materials that are of great interest in both fundamental and application-oriented research [22]. Based on temperature variations, charge transport, the molecule, collective dipolar fluctuations, and polarisation effects at inner phase boundaries were studied. is article reports the impedance and modulus spectroscopic investigations in detail as a continuation of our prior work on the dielectric constant and dielectric loss as a function of frequency. e resistive property of the grown crystals can be obtained from dielectric studies. e measured dielectric properties are primarily related to the electro-optical properties of an optical single crystal [23]. It further gives insight into the charge transportation properties and charge storage capabilities of the dielectric material. e electronic industries require materials with a low dielectric constant that can be used as a dielectric interlayer during microelectronic device fabrication [24,25].  Figure 4 shows that the decreasing trend in dielectric loss with increasing frequency suggests that the optical quality of the formed 3NPTAT crystal is good with few imperfections, making it appropriate for photonics, laser, and electro-optic device manufacturing. e fact that the dielectric constant and dielectric loss are reduced at higher frequencies indicates that the formed crystal contains a small number of electrically active flaws, which is important in NLO applications [26]. Figures 5 and 6 show the frequency-dependent real (ε′) and imaginary (ε") parts of the dielectric constant at various temperatures, including 313 K, 333 K, 353 K, and 373 K. e ability to retain electrical energy is the real component of dielectric, whereas the ability to lose electrical energy owing to fluctuations in an applied electric field is the imaginary part. Excellent insulating properties are found in materials with a high dielectric constant and low dielectric loss (tan δ). Figure 6 shows that at low frequencies, the obtained high dielectric constant (ε r) values are due to interfacial or space charge polarisations. It can also be seen that at all temperatures, the real part of the dielectric constant (ε′) decreases with increasing frequency and reaches a maximum value at high frequencies.

Frequency Dependence of Real and Imaginary Parts of Dielectric Constant.
e increase in conductivity of the material at high frequencies is caused by a decreasing trend in the imaginary part of the dielectric constant, as shown in Figure 7, which is  similar to the earlier report [27]. At low frequencies, the grain boundary effect would be more pronounced. e effect of dielectric polarisation is caused by electrons/holes hopping between both the positive and negative surface defect centers in the grain boundary region at low frequencies. At 373 K, the imaginary dielectric constant is high, indicating that the imaginary part of the dielectric constant (ε′) grows as temperature rises, although the real dielectric constant (ε′) is high at 353 K. At high temperatures, larger grains form, lowering the energy barrier and accelerating atom diffusion to another grain in a single crystal. According to the findings, all types of polarisation (electronic, ionic, orientation, and space charge) play a significant role, but electronic polarisation is the most important [28].

Complex Impedance Spectroscopic Studies.
Complex impedance spectroscopy techniques can be employed to circumvent the restrictions in frequency-dependent dielectric constant and dielectric loss [29][30][31][32][33][34]. To understand the dielectric behavior and electrical conductivity of materials, the Cole-Cole plot is commonly used in impedance spectroscopic studies to determine the variation among various parameters such as permittivity, impedance, electric modulus, and tangent loss as a function of frequency [35]. e microstructure level of the material can be determined via a complex impedance spectroscopy investigation. It aids in determining how charge transfer occurs in the material as well as how much it relaxes. e response at high frequency is attributable to grains, while the response at low frequency is due to grain boundaries, according to impedance data from the dielectric system plotted in the complex plane. e complex impedance spectra of 3NPTAT at various temperatures are shown in Figure 9. At all temperatures, all of the samples have a single semicircle shape, as shown in Figure 9. e linear representation of bulk resistivity is given by the semicircle on the real axis. e semicircle represents a grain boundary effect for 3NPTAT at 373 K, with the decrease in impedance value due to increased grain size or grain growth [32,33]. Figure 10 shows how to compute the activation energy for the thermodynamic system Z. Table 1 shows the activation energy derived from different    Advances in Condensed Matter Physics frequencies based on the imaginary impedance of singlecrystal 3NPTAT. Table 1 shows that the activation energy value for a particular frequency above 1 MHz is in the range of 0.02-0.03 eV, whereas for lower frequencies below 1 MHz, the value is greater (0.04-0.07 eV). At low frequencies, charge carriers are thought to travel a great distance and are restricted to a potential well at high frequencies [27,30].

Dielectric Modulus Studies.
Sinclair and West explained that to understand the dielectric properties of a given material, both complex impedance and modulus investigations are used [31]. e grain boundary effect and the conduction mechanism were distinguished using a complex dielectric modulus analysis. e real and imaginary plots of frequencydependent electric modulus by altering the measurement temperature are shown in Figures 11 and 12. M′ increases with frequency, reaches a peak at 0.45 rad/s, and then steadily falls at high frequencies, indicating the semiconductor property. Because of the short-range mobility of ion charges and their confinement in the potential well, the asymmetric real electric modulus shifts towards higher frequency regions [27]. Furthermore, at low frequencies, the real component of the dielectric modulus is low, implying that electrode polarisation is minimal.
When compared to dielectric loss, the imaginary portion of the dielectric modulus is utilized to characterize the relaxation nature of the materials. e obtained modulus plot shows that electrical relaxation occurs in the produced crystal. At room temperature, the complex moduli of the M′ and M″ series draw semicircles in the complex plane. e two depressed semicircular graphs for the 3NPTAT crystal recorded at 373 K are shown in Figure 13. e linear spikes in the low-frequency band of the Nyquist plot in Figure 13 indicate a supercapacitive nature. is happens because the ions in the electrolyte intercalate and pass through the electrode [36][37][38]. e conductivity relaxation's peak breadth indicates that the single relaxation time is related to the Debye process. Figure 14 shows a conductivity relaxation peak in the M" vs log (f ) curve, which shows a minor shift towards higher frequency with increasing 3NPTAT concentration. e shorter relaxation time (τ �1/fmax) and greater polaronic hopping rate in the concentration of 3NPTAT are related to the rise in peak frequency. e charts plainly illustrate that the arcs' centers do not correspond to the real axis. e first semicircle is due to  Advances in Condensed Matter Physics the grain boundary effect at lower frequencies, although this impact is not visible in the impedance plot or Nyquist plot at higher frequencies.
A Bode plot is a graph that shows the amplitude and phase of a transfer function in a linear system on a logarithmic scale. Figure 15 depicts the fluctuation of the Bode phase angle concerning applied angular frequency (Bode plots). In an EIS Bode plot, the crystal has nearly the same morphology across the whole frequency range and for all temperature measurements. For all the samples examined at different temperatures, a higher phase angle close to 90°was seen at low frequency (a feature of an ideal capacitor). is corresponds to the cell's capacitive functionality. e appearance of a single peak over the whole frequency range shows the presence of grain effects for the generated single-crystal 3NPTAT. e dielectric characteristics of the materials are altered by grain effects. We can adjust the dielectric characteristics by changing the grain size of dielectric materials by varying parameters such as growth temperature, stoichiometric composition, postsintering temperature, and so on. e ac conductivity is determined using the following formula: where C is the capacitance, d is the crystal thickness, A is the crystal area of cross-section, and f is the applied field frequency. Figure 16 shows the frequency dependence of electrical conductivity at various temperatures. It signifies that as frequency rises, conductivity rises as well, following Jonscher's universal power law.   Advances in Condensed Matter Physics σ o is the frequency-independent conductivity; σ ω is the frequency-dependent conductivity, which is expressed as follows: Here, ω is the angular frequency of the applied ac field.
Conductivity is essentially nonexistent up to 3 MHz. Beyond 3 MHz, conductivity rises and yields a slope at hopping frequency, indicating that the formed 3NPTAT crystal is thermally active [39].

Conclusion
In the frequency range of 50 Hz to 5 MHz, the dielectric and charge transport properties of the synthesized nonlinear optical material 3NPTAT single crystal were investigated at four different temperatures 313 K, 333 K, 353 K, and 373 K. e determined dielectric constant ′ and dielectric loss ′′ showed decreasing trends with frequency elsewhere. e influence of the electric field on the dipoles explained the drop in ε′. At low frequencies, these dipole moments easily follow the direction of the alternating applied field, resulting in significant polarisation values, as shown by high values of ε′. However, at high frequencies, dipoles have difficulties following the field's direction, polarisation weakens, and constant dielectric ε′ values fall. After analyzing the data, it was shown that charge transportation relaxation and hopping mechanisms occur at low temperatures with concentrated charge carriers. e results also show that the grain boundary effect causes a single relaxation process at a high frequency. e increase in modulus with frequency attains the maximum value again, and a decrease in modulus shows the semiconducting character. is trend also shows that the relaxation mechanism is dominated by dipole orientation relaxation under the influence of the electric field. e combination of impedance spectroscopy and modulus yields a lot of information on the electrical relaxation process in the microstructure of materials. At higher frequencies, the activation energy is determined to be 8-36 eV, which explains relaxation in the lower region, where charge carriers are stable and can travel long distances. 3NPTAT is activated at high temperatures according to the frequency-dependent electrical conductivity measurements, and the material exhibits a low dielectric loss and a high dielectric constant. As a result, possible dielectric relaxations, conduction mechanisms, and the electrical field effect were examined in the context of this formalism. According to the findings, the produced 3NPTAT single crystal acts as a perfect insulator and a superior dielectric material for high-frequency device applications.
Data Availability e authors confirm that the data supporting the findings of this study are available within the article.

Conflicts of Interest
e authors declare that there are no conflicts of interest.