Impact of high NiO content on the structural, optical, and dielectric properties of calcium lithium silicate glasses

J Mater Sci: Mater Electron Impact of high NiO content on the structural, optical, and dielectric properties of calcium lithium silicate glasses S. Ibrahim1, H. A. Abo-Mosallam1, Ebrahim A. Mahdy1,* 1 2 , and Gamal M. Turky2 Glass Research Department, National Research Centre, 33El-Buhouth St, Dokki 12622, Cairo, Egypt Department of Microwave Physics & Dielectrics, National Research Centre, 33El-Buhouth St, Dokki 12622, Cairo, Egypt Received: 26 January 2022 ABSTRACT Accepted: 5 March 2022 Glasses with the composition (11.5 - 9) CaO - 23.5Li2O - 65SiO2: 9 NiO mol. % (0    11.5) were synthesized by melt-quenching method. And a number of physical parameters have been established. The refractive index and energy gap were also used to estimate the metallization criterion, where these glasses have shown values fallings between high (insulators) and low (metals), indicating that they are semiconductors. The XRD pattern shows the amorphous nature of investigated glasses. A number of spectroscopic analyses of the studied glasses were performed, in relation to NiO content, including Fourier transform infrared (FTIR) and UV–Visible diffuse reflectance spectroscopy (DRS). Due to compositional changes, FTIR measurements have revealed structural changes in the glass network. Furthermore, with increasing NiO content, the asymmetrical bands of silicate units increase. The creation of Ni–O– Si bonds in the silicate matrix has been attributed to the introducing heavier Ni?2 as [NiO4]2- tetrahedral species in substitution of the lighter silicon ion in the [SiO4]4- network, but it could also operate as a network modifier in glass materials. The Ni2? ion may have behaved as a network intermediary, causing more compact structure. The mechanism of charge transfer in the glass compositions under investigation is studied using broadband dielectric spectroscopy. For the first time, the relationship between the hopping time of free ions and dc conductivity is illustrated. All of the glasses under investigation have the same charge transport mechanism. The results suggest the semiconducting nature of these glasses. Ó The Author(s) 2022 Address correspondence to E-mail: ; https://doi.org/10.1007/s10854-022-08045-8 J Mater Sci: Mater Electron 1 Introduction Lithium based-silicate glasses are widely recognized as photosensitive glasses [1]. They are thermally, chemically, and mechanically stable, making them a perfect host for transition metal ions with intense luminescence in the visible region [1, 2]. In amorphous matrices, nickel ions are very stable and mainly occupy octahedral sites. The spectroscopic properties of Ni2þ ions in glasses are remarkable due to their high stability, and various intensive investigations into these materials are present in the literature [3–5]. In glass materials, a portion of Ni2þ ions may occupy tetrahedral positions, besides octahedral occupation. Quantitative properties of modifiers and glass formers, as well as their field strength, the size of the ions in the glass matrix, modifier cation motion, and other factors, all influence the concentration of ions in tetrahedral or octahedral sites [6]. The octahedral nickel ions function as modifiers, generating structural flaws, whereas the tetrahedral ions combine with the basic glass network. The physical properties of the host glass material, particularly its electrical properties, are likely to be influenced by the movement of nickel ions between these two sites [7]. The electron configuration of the transition metal nickel ions causes the shell layer being3d8 4s0 , transitions among Ni2þ ions d orbits are more sensitive to matrix changes [8]. Nickel oxide has been the subject of several scientific studies, particularly due to its remarkable optical, electrical, and magnetic properties [9]. NiO is a ptype semiconductor prototype with a 3.6–4.0 eV broad bandgap [10]. Before being employed in perovskite solar cells (PSCs), nickel oxide was used as the p-type hole transport layers (HTL) in dye-sensitized solar cells (DSSCs) and organic photovoltaics (OPV). NiOx has a high transparency due to its wide bandgap (3.6 eV), deep valence band (- 5.2 to - 5.4 eV), and high carrier mobility (0.1 cm2/Vs), as well as good light, heat, and moisture stability, making it a good candidate for hole transport layers (HTL) in perovskite solar cells (PSCs). Using a lowtemperature combustion technique, copper-doped NiOx (Cu:NiOx) achieved efficiencies of over 17.8%, outperforming the traditional sol–gel-derived hightemperature Cu:NiOx PCE of 15.5%. Thus, various elements such as Cu, Li, Mg, Cs, and Co can be doped into NiOx to improve conductivity and PSC efficiency by lowering interfacial resistance at the HTL/perovskite interface [11]. The electronic features of NiO have benefited anodes for lithium-ion batteries, electrochromic coatings, solar cells, antiferromagnetic materials, composite anodes for fuel cells, and chemical (gas) sensors. NiO is also examined, into that, for applications such as electrochemical devices, supercapacitors, smart windows, and dye-sensitive photocathodes [12]. The transparent glasses and ceramics doped with NiO have received interest for use in broadband optical amplifiers and tunable lasers due to its broad and extended emission in the wavelength spectrum covering the whole optical communication windows [13–15]. Both tetrahedral and octahedral positions in the glass network are occupied by nickel ions, when they are incorporated into base glass [16], and produce different colors depending on the equilibrium between nickel ions in the sixfold NiO6 and fourfold NiO4 coordination [17]. Ion concentration in the tetrahedral or octahedral positions is affected by the composition and type of the host glass [18]. Among others, the Broadband Dielectric Spectroscopy (BDS) has recently been considered as a very useful tool for probing charge carriers’ transport as well as the different kinds of molecular dynamics in all condensed matters. This is because it can probe the molecular fluctuations and charge transport in broad ranges of frequency and temperatures. Nickel oxide plays a very well role in traditional glasses in small amounts. Earlier researchers [19–21] investigated the optical, redox (Ni/Ni2?), and magnetic properties of nickel-contained glasses with low NiO contents. Also, Smith et al. [22] used neutron diffraction to investigate the structural characterization of bioactive glasses doped with 4.0 mol% NiO and found Ni–O–Si bonding in the silicate network, with one third of the Ni2? ion occupying a network forming tetrahedral geometry and the other two thirds occupying a fivefold coordination in the bioglass. Finally, Suresh et al. [23] studied the spectroscopic characteristics of lead–bismuth–silicate glasses containing 0–1.0 mol. % NiO and found that Ni2? ions were present in the glass in both octahedral and tetrahedral symmetries. According to the authors, increasing the concentrat (...truncated)