PHYSICS AND CHEMISTRY OF SOLID STATE

The peculiarities of the structure and phase composition of the high-entropy alloy of the TiCrFeMnSiC system obtained from the powder mixture of ferrotitanium, ferrochrome and ferrosilicon-manganese ferroalloys are considered in the work. The technological scheme of alloy production included joint grinding of the mixture in a planetary mill, consolidation of the blanks, their heating to 1100 C, hot forging on the dugostator press and subsequent annealing of hot-forged samples at 1200 C. According to the results of X-ray analysis of the obtained alloy, it was found that the main phase of the alloy is the BCC phase with the parameter of the cubic lattice a = 0.2868 nm, which is a solid solution based on alloying components of the original charge. The phase composition of the composite also recorded titanium carbide TiC with FCC lattice with the parameter a = 0.4319 nm, which corresponds to a stoichiometric composition of about TiC0.6 and a small amount of FCC phase of iron-chromium carbide (Cr, Fe)23C6 with lattice parameter a = 1.0645 nm. The material has a high hardness (up to 60-61 HRC), which can provide high resistance of this multicomponent alloy.


Introduction
The new polymer nanocomposites production has been commonly studied by the modern fields on nanoscale inorganic additive in the food packaging approaches, barrier fields, coatings, antimicrobial, sensors, antiballistic products, conductive, and other materials. The novel generation of these nanocomposites includes carbides (B4C, SiC, WC), nitrides (BN CrN, TiN, ZrN), borides (CrB2, ZrB2,WB, TiB2), metal oxides (Y2O3, MgO, Al2O3, ZrO2, CeO2, Fe2O3, SiO2, TiO2), cellulose nanofibrils, carbon nanotubes, and other nanoparticles types as scatter phase. The properties and characteristics of the new nanomaterials are affected by the kind of additive employed by the polymer matrix. The applications include many fields like electronics, aerospace, military, vehicles, marine and medicine [1]. The transition metals oxides are an significant group of semiconductors have functions in solar energy transformation, magnetic storage media, catalysis and electronics [2]. MnO2 is promising green matter has involved large interests in good quality of its excellent environmental compatibility, low cost, and broad structural diversity combined with especial chemical and physical characteristics. The important fields of MnO2 nano-scale contain alkaline batteries, gas sensors, photocatalyst, electrochemical capacitors, and smart windows [3].Polyvinyl alcohol is an important polymer, relate to its chemical and physical features. This polymer may be a film, powder, and fiber forms. PVA has a semi-crystalline nature due from the hydrogen bonds and the OH group role. Relate to its low protein adsorption properties, excellent water solubility and biocompatibility, PVA is usually employed in medical devices. Polyvinylpyrrolidone has a excellent stable environment, moderate electric conductivity and easy processing. PVP has a broad applications range like electrochemical devices. PVA/PVP interactions have unique characteristics which combine the characteristics of both polymers [4]. The present work aims to prepare the PVA/PVP/MnO2 nanostructures films to use as lightweight and low-cost pressure sensors.

I. Materials and Methods
Nanocomposites films of polyvinyl alcohol (PVA)polyvinyl pyrrolidone (PVP)-manganese oxide (MnO2) was fabricated by using casting method. The solution of PVA/PVP blend was prepared by the 0.5 gm of PVA and PVP with ratio 77 wt.% PVA: 23 wt.% PVP were dissolved in distilled water (20 ml) of. The MnO2 NPs added to the blend with ratios are 1.5 %, 3 % and 4.5 %. The optical characteristics measured in range of wavelength (220 -820) nm by spectrophotometer (UV/1800/ Shimadzu). The dielectric characteristics of films measured in frequency range (100 Hz -5 ×10 6 Hz) by LCR meter type (HIOKI 3532-50 LCR HI TESTER). The pressure sensor testing investigated by measuring the capacitance between two electrodes on the top and bottom of the sample for various pressures range (80 -200) bar. The absorption coefficient (α) is given by [5,6]: where A: absorbance and t: sample thickness. The energy band gap can be determined by [7]: where B: constant, hυ: photon energy, Eg: energy band gap, r = 3 for forbidden indirect transition and r = 2 for allowed indirect transition. The refractive index (n) is given by [8]: where R is the reflectance. The extinction coefficient (k) is defined by [9]: where λ is the wavelength of incident photon. The dielectric constant parts: real (ε1), and imaginary (ε2) are calculated by the equations [10]: The optical conductivity (σop) can be calculated by the equation [11].
The dielectric constant (έ) is given by the equation [12]: where, Cp is parallel capacitance and Co is vacuum capacitor The dielectric loss (ε˝) can be calculated by using [13]: where D is dispersion factor. The AC electrical conductivity can be determined by using [14]: σA.C= w ε ˝εₒ, where wangular frequency. Figure 1 shows the FTIR measurements of PVA/PVP/MnO2 nanostructures. As shown in Figure 1, there is no interactions between the blend and the MnO2 NPs. It shows broad bands at around 3257 cm -1 are observed related to OH groups in the blend chain. The peaks at around 1647 cm -1 due to the presence of such free C=O groups. The bands at around 1289 cm -1 due to the other bonds (C-O-C) [15].

II. Results and Discussion
The behavior of absorbance of pure polymeric blend and PVA/PVP/MnO2 nanostructures with wavelength is shown in Figure 2. The absorbance of blend is rise with the increase in MnO2 NPs content; this is relate to rise of the charges carries numbers [16,17].
The absorption coefficient is useful to show the electron transition nature. The PVA/PVP/MnO2 nanostructures has values of absorption coefficient less than (10 4 cm -1 ) as shown in Figure 2. The absorption coefficient of PVA/PVP/MnO2 nanostructures is rise with the rise of MnO2 NPs content which related to rise the charges carries numbers [18], as shown in Figure 3. Figure  3 indicates that the nanoparticles shape a continuous arrangement within the polymeric blend at high ratios [19,20]. These overlaps offer evidence for reducing energy band gap when the MnO2 NPs ratio rise in the polymeric blend [21].
The variation of extinction coefficient and refractive index with wavelength of films are shown in Figures 6 and  7 respectively. The figures indicate that the extinction coefficient and refractive index of blend are rise with the rise in MnO2 NPs ratio. The rise of extinction coefficient and refractive index of blend related to rise the absorption coefficient and the samples density [22][23][24][25]. Figures 8 and 9 indicate to the real and imaginary of dielectric constant behavior with wavelength respectively. The real part mostly depends on n 2 because   [26]. Figure 10 represents the optical conductivity variation of PVA/PVP/MnO2 nanostructures with wavelength. The optical conductivity of blend rises with the increase in MnO2 NPs ratio and photon energy. The rise in optical conductivity as MnO2 NPs ratio increase due to reduce the energy gap [27][28].      [29,30]. The dielectric constant and dielectric loss reduce while the conductivity rises with the rise in frequency; this is due to the polarization effects [31]. The variation of capacitance for PVA/PVP/MnO2 nanostructures films with pressure is shown in Figure 4. The figure indicates that the capacitance rises with the rise in pressure. When the pressure is applied to film, it led to mechanical deformation and charges displacement. An electric field will produce and consequently voltage may be detected on the lower and upper film surface. When stress is removed, the voltage will disappear. This fact is called direct piezoelectric effect. Conversely, the internal production of mechanical strain of the film resulting from an applied electrical field is called reverse piezoelectric effect [32].

Conclusions
The results of optical characteristics showed that the optical absorbance of PVA/PVP blend rises with the rise in the MnO2 NPs ratio. The energy gap of blend reduces with the rise in MnO2 NPs content. The optical constants