ZnFe2O4 composite with assorted composition ratios

Journal Pre-proof In situ formation, structural, mechanical and in vitro analysis of ZrO2/ZnFe2O4 composite with assorted composition ratios

Subina Raveendran, M. Mushtaq Alam, Mohd. Imran K. Khan, Arunkumar Dhayalan, S. Kannan PII:

S0928-4931(19)33059-0

DOI:

https://doi.org/10.1016/j.msec.2019.110504

Reference:

MSC 110504

To appear in:

Materials Science & Engineering C

Received date:

19 August 2019

Revised date:

5 November 2019

Accepted date:

27 November 2019

Please cite this article as: S. Raveendran, M.M. Alam, M.I.K. Khan, et al., In situ formation, structural, mechanical and in vitro analysis of ZrO2/ZnFe2O4 composite with assorted composition ratios, Materials Science & Engineering C (2018), https://doi.org/ 10.1016/j.msec.2019.110504

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© 2018 Published by Elsevier.

Journal Pre-proof

In situ formation, structural, mechanical and in vitro analysis of ZrO2/ZnFe2O4 composite with assorted composition ratios

Subina Raveendrana, M. Mushtaq Alama, Mohd. Imran K. Khanb, Arunkumar Dhayalanb and S. Kannana a

Centre for Nanoscience and Technology,

Pondicherry University, Puducherry-605 014, INDIA Department of Biotechnology,

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b

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Pondicherry University, Puducherry-605 014, INDIA

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Corresponding Author’s Address

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Dr. S. Kannan Centre for Nanoscience and Technology,

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Pondicherry University, Puducherry-605014, INDIA E-mail: [email protected],

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Phone: 0091-413-2654973

Journal Pre-proof Abstract The investigation underline the in situ formation of ZrO2/ZnFe2O4 composites and the resultant structural, morphological, mechanical and magnetic properties. The characterization results ensured the crystallization of tetragonal ZrO2 (t-ZrO2) and ZnFe2O4 phases at 900 °C. Depending on Zn2+/Fe3+ content, the composite system revealed a gradual increment in the phase yield of ZnFe2O4. The significance of monoclinic ZrO2 (m-ZrO2) is also evident in all the systems at 900 °C; however, the incremental heat treatment to 1300 °C indicated its corresponding loss, thus

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indicating the reverse m-  t-ZrO2 transition. The crystallization of ZnFe2O4 as a secondary

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phase in the t-ZrO2 matrix is also affirmed from the morphological analysis. Mechanical studies

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accomplished good uniformity in all the investigated compositions despite the variation in the

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phase content of ZnFe2O4 in composite system. All the t-ZrO2/ZnFe2O4 composites ensured strong ferrimagnetic features and moreover better biocompatibility and non-toxicity

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characteristics were displayed from in vitro tests.

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Key words: t-ZrO2; ZnFe2O4; Structure; Mechanical; Magnetic; In vitro.

Journal Pre-proof 1.

Introduction

Recent studies highlight the importance of magnetic bioceramics in the field of hyperthermia for osteosarcoma. The concept of hyperthermia is mainly based on employing magnetic materials to induce heat in the range of 41- 46 ºC at the bone tumor site, in response to an external magnetic field [1–4]. A synthetic bone substitute that possess the additional feature to destroy tumor cells is expected to be an ideal candidate to treat osteosarcoma [5]. Biomaterials such as hydroxyapatite [HAP, Ca10(PO4)6(OH)2], β-tricalcium phosphate [β-TCP, β-Ca3(PO4)2], zirconia

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(ZrO2) and alumina (Al2O3) are extensively reported to treat bone related disorders [6–12]. On

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the contrary, magnetic nanoparticles such as iron oxide (Fe 3O4) and face-centered cubic (FCC)

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close packed spinel ferrites namely NiFe2O4, MnFe2O4 and CoFe2O4 deliberate enhanced magnetic features for hyperthermia application [13–16]. Moreover, the competence of MFe2O4

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(M = Ni2+, Mn2+ and Co2+) in biomedical applications also depends on the fabrication methods,

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chemical stability and magnetic tuning ability [17–23]. Notwithstanding the availability of

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reports that substantiate the magnetic efficacy of MFe2O4, the drawback of structural degradation experienced at elevated heat treatments remain a major concern [24,25]. Among the

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various MFe2O4, ZnFe2O4 with salient features of high electromagnetic performance, excellent

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chemical stability, mechanical hardness, low coercivity, and moderate saturation magnetization makes it a good contender for hyperthermia applications [26–28].

Magnetic characteristics in HAP and β-TCP bioceramics imparted through the integration of a suitable magnetic component receives profound interest during recent years. Reports accomplish the importance of magnetic bioceramics to persuade pronounced hyperthermia efficiency together with the exceptional biocompatible features [29–31]. Despite the convincing feature of magnetic bioceramics to ensure profound hyperthermia efficiency, the lack of mechanical compatibility to fulfill the basic requirements of a bone substitute remains a major concern. In this context, the exceptional mechanical features of ZrO2 bioceramic has been considered as an

Journal Pre-proof effective bone substitute as it possess a greater propensity to withstand severe wound contraction forces at the defective bone site [32]. Amongst the three different ZrO2 polymorphs namely monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2) and cubic zirconia (c-ZrO2), the exceptional mechanical features of t-ZrO2 and c-ZrO2 are highly preferred in load bearing orthopedic applications [33,34]. The constraint to stabilize room temperature t-ZrO2 and c-ZrO2 is generally rectified with the aid of stabilizers such as Y 2O3, MgO, CaO and La2O3 [8,35–38]. Y2O3 stabilized ZrO2 with exceptional mechanical features are more commonly used in

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biomedical applications [39–43].

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Thus, combining the exceptional magnetic feature of ZnFe2O4 and mechanically stable ZrO2 in the composite form is expected to elicit dual features of mechanical biocompatibility and

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pronounced magnetic efficacy. The present investigation aims to form ZrO2/ZnFe2O4 composite

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with varied compositional ratios through a solution based synthetic approach. The variation in

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the concentrations of Zn2+/Fe3+ to induce structural change in ZrO2, the ability to retain structurally stable polymorphs of ZrO2 and ZnFe2O4 at elevated temperatures are explored.

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Further, the magnetic, mechanical and in vitro biocompatibility efficacy of the resultant

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ZrO2/ZnFe2O4 composites are tested.

2.

Material and methods

2.1

Powder Synthesis

The synthetic technique to yield ZrO2/ZnFe2O4 composite is accomplished through sol-gel method.

Analytical

grade

zirconium

oxychloride

[ZrOCl2.8H2O],

ferric

nitrate

[Fe(NO3)3.9H2O], zinc nitrate [Zn(NO3)2.6H2O] and yittrium nitrate [Y(NO3)3.6H2O] were used as precursors and citric acid (C6H8O7) has been used as a fuel to catalyze the reaction process. Five different Zn2+/Fe3+ combinations with respect to the constant concentration of ZrO2 were synthesized. In addition to these combinations, stoichiometric ZrO2, Fe3+ only and Zn2+ only

Journal Pre-proof substitutions in ZrO2 were also synthesized for comparative purpose. Moreover 8 mol. % Y3+ with respect to the Zr4+ concentration has been used as a stabilizer in all the compositions. All synthesis that involve the combined addition of Zn2+/Fe3+ in ZrO2 were performed with equimolar concentrations of Zn2+ and Fe3+, which have been fixed based on the comparatively better affinity displayed by Zn2+ than Fe3+ towards ZrO2 lattice. The precursor concentrations along with their sample codes are illustrated in Table 1. In a brief description of the synthesis, the individual stock solutions of ZrOCl2, Fe(NO3)3, Zn(NO3)2 and Y(NO3)3 were mixed together

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under constant stirring conditions at 90 ºC and this was followed by the addition of citric acid to

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the reaction mixture after 10 min. The resultant mixture was stirred continuously to attain a

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viscous gel and subsequently dried overnight at 120 °C. The synthesized powders were heat treated at predetermined temperatures (CARBOLITE GERO, RHF 1600) with a dwell time of 2

Characterization methods

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2.2

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h and were subjected to analytical characterization.

The phase analysis of the heat treated powders were determined using high resolution X-ray

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diffractometer (RIGAKU, ULTIMA IV, JAPAN) with Cu Kα radiation (λ=1.5406 Å) produced

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at 40 kV and 30 mA to scan the diffraction angles (2θ) between 5º and 90° with a step size of 0.02º, 2θ per second. Standard ICDD [International Centre for Diffraction Data] card Nos. 98002-7987, 98-004-7563 and 98-004-0456 were used for the phase analysis of t-zirconia (t-ZrO2), m-zirconia (m-ZrO2), and ZnFe2O4 respectively. GSAS-EXPGUI software was used to perform the structure refinement of powder XRD data and the refinement procedure was performed in accordance with the previous studies [37,44]. The crystallographic information files (CIF) from Howard et al, Smith et al, Finger et al and Hugh et al, were respectively taken as standards to refine t-ZrO2, m-ZrO2, -Fe2O3 and ZnFe2O4 structures [45–48].

Journal Pre-proof Confocal Raman microscope (RENISHAW, United Kingdom) was used to analyze the vibrational modes of the powder specimens with the conditions of excitation at 785 nm, semiconductor diode laser with power of 0.5 % and data acquiring time of 30s. Physical property measurement System (PPMS; Quantum Design, San Diego, CA, USA) in VSM (vibrating sample magnetometer) mode was used to measure the magnetic hysteresis under the applied magnetic field of ± 1T tesla at room temperature (300 K). The compositional and chemical state analysis has been determined through X-ray photoelectron spectroscopy (XPS,

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AXIS ULTRA). The binding energy calibrations for the shift in charge were calibrated using the

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C 1s peak of graphitic carbon (BE = 284.8 eV) as standard.

Mechanical properties

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The mechanical properties of all the t-ZrO2/ZnFe2O4 composites were carried out at room

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temperature using Nanoindenter machine (BRUKER, USA) in accordance with the procedure

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described elsewhere [49,50]. In brief explanation of the indentation procedure, the synthesized powders were annealed at 700 °C and subsequently milled using a high planetary ball

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(RETSCH, GERMANY). The resultant powders were pressed to a specimen size of 10 mm

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diameter and 1 mm thickness with the help of semi-automatic hydraulic press (KIMAYA ENGINEERS, INDIA) under an applied force of 5 kN for 60 sec. The resultant specimens were treated at 1300 °C with a dwell time of 2 h followed by a fine polishing using a diamond paste before the indentation procedure. The tests with a single indent mode at 10 different locations with an applied load of 5 mN was done for all the specimens. A conventional depth-sensing test with a measurement cycle (load/unload displacement curves) consisted of a loading segment followed by a dwell time at maximum load; finally an unloading segment was used to determine the selective mechanical properties. The microstructures of the sintered specimens were determined through field emission scanning electron microscope (FESEM, CARL ZEISS

Journal Pre-proof MICROSCOPY). The protocol for the in vitro biological evaluation (cell viability assay, livedead assay and relative ALP expression) are described in Supporting Information S1.

3.

Results

3.1

Phase analysis

The structural ability of 8 mol.% Y2O3 stabilized t-ZrO2 (8YSZ) at elevated temperatures is well-documented [8,42,51]. Initially, the phase behavior of 8YSZ in the presence of Zn2+/Fe3+

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during progressive heat treatments were tested to determine the appropriate temperature to yield

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the desired t-ZrO2/ZnFe2O4 composite. XRD patterns (Figure 1a) recorded after treatment at 900

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°C unveiled the presence of m-ZrO2, t-ZrO2 and ZnFe2O4 mixtures in all the compositions.

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Moreover, the incidence of -Fe2O3 reflections has also been obvious in 60ZFZ and 100ZFZ. A similar phase behavior is noticed for the XRD patterns recorded at 1100 °C (Figure 1b) while

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the sharp variations were determined in the patterns recorded at 1300 °C (Figure 1c). The

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presence of t-ZrO2 and ZnFe2O4 reflections were noticed in 40ZFZ while the trace of m-ZrO2 peaks alongside the dominant intensity reflections of t-ZrO2 and ZnFe2O4 are witnessed in

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10ZFZ and 20ZFZ. Despite the presence of t-ZrO2 and ZnFe2O4, the minor reflections of -

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Fe2O3 were also noticed in 60ZFZ and 100ZFZ.

The phase behavior of Zn2+/Fe3+ combine in ZrO2 is also verified with the aid of two different alternative compositions namely Zn2+ only and Fe3+ only substitutions in 8YSZ (Supporting Information S2 and S3). Zn2+ only addition revealed t-ZrO2, Y2O3 and ZnO phase mixtures in all the temperatures of 900, 1100 and 1300 °C. Despite the addition of Zn2+ in two different concentrations, the phase behavior has been the same at all the temperatures except the enhanced reflections of ZnO determined in high Zn2+ concentrations. Whereas the Fe3+ only substitutions in 8YSZ revealed a contrasting behavior in comparison with its Zn2+ counterpart. Low amount of Fe3+ substitutions yielded t-ZrO2 and YFeO3 at all the temperatures while the

Journal Pre-proof incidence of m-ZrO2 reflections has been determined in the decreasing order during progressive heat treatments at 1100 and 1300 °C. Fe3+ substitutions at high level unveiled t-ZrO2, -Fe2O3 and YFeO3 phases mixtures at 900 °C whereas m-ZrO2 reflections has been determined as an additional component in the decreasing order during progressive heat treatments at 1100 and 1300 °C.

3.2

Raman spectra

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Raman spectra recorded at three different temperatures (Figure 2) established good consistency

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with XRD results. In particular, the spectra recorded at 1300 °C (Figure 2c) revealed the

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presence of various bands in all the compositions at 148, 181, 224, 266, 317, 335, 358, 385, 474, 496 and 630 cm-1. These bands attribute to the presence of four different structures namely t-

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ZrO2, m-ZrO2, ZnFe2O4 and -Fe2O3. In particular, the dominant bands at 148, 266, 317, 385,

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474 and 630 cm-1 pertinent to t-ZrO2 are invariably detected in all the compositions [52].

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However, the typical ZnFe2O4 bands  355 cm-1 were detected in all the systems excluding 10ZFZ [53,54]. The increment in the intensity of this particular ZnFe2O4 band is obvious in the

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order of 20ZFZ, 40ZFZ, 60ZFZ and 100ZFZ. Further, an additional band  224 cm-1 typical of

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ZnFe2O4 is also detected in 100ZFZ that possessed excess Zn2+/Fe3+ content. In general, the cubic spinel crystal structure of ZnFe2O4 exhibit five different Raman active modes (3F2g+Eg+ A1g) [55]. Raman active A1g mode is unveiled > 600 cm-1 due to the oxygen motion in tetrahedral co-ordination of ZnO4 groups while the bands < 600 cm-1 originate from the octahedral coordination of FeO6 groups. Raman spectra also specify the presence of bands 180 and  335 cm-1 representative of m-ZrO2 in 10ZFZ and 20ZFZ that exhibited good concurrence with the literature values [52,56]. The simultaneous decline of m-ZrO2 bands and the obvious upsurge in ZnFe2O4 bands from 40ZFZ ascertain the formation of composite structures based on t-

Journal Pre-proof ZrO2/ZnFe2O4. In the meanwhile, the hematite (-Fe2O3) band at 496 cm-1 is detected in 100ZFZ [57].

3.3

Structure refinement

In continuation with the qualitative XRD analysis, the influence of wide range of Zn2+/Fe3+ additions in ZrO2 were determined through the structure refinement of powder XRD patterns. The selective refined diffraction patterns are presented in Figure 3 and the corresponding phase

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composition, structural parameters and crystallite size are presented in Tables 2 and 3. The

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crystallization of t-ZrO2, m-ZrO2, ZnFe2O4, and -Fe2O3 in their respective tetragonal (P42/nmc

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(137) space setting), monoclinic (P42/nmc (137) space setting), cubic spinel (Fd-3m(227)) space

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setting) and hexagonal [R-3c(167) space setting] were confirmed from the structure refinement. The phase fraction data at 900 °C revealed a gradual increment in t-ZrO2 alongside a

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simultaneous decline in the m-ZrO2 content as a function of enhanced Zn2+/Fe3+ content. The

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phase fraction of ZnFe2O4 also deliberated an enhanced trend with respect to the progressive Zn2+/Fe3+ additions at 900 °C. Moreover, the evidence of -Fe2O3 trace is also obvious in

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60ZFZ and 100ZFZ at 900 °C. A similar observation on the phase fraction data is also noticed at

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1100 °C; however, with relatively an enriched phase content of t-ZrO2. While the complete absence of m-ZrO2 in 40ZFZ, 60ZFZ and 100ZFZ and the presence of -Fe2O3 trace in 60ZFZ and 100ZFZ were determined at 1300 °C. The desired t-ZrO2 and ZnFe2O4 mixtures were accomplished only in 40ZFZ. The refined lattice parameters of t-ZrO2 indicated a sharp decline on comparison with the data of 8YSZ. Moreover, a gradual decline in both a-=b-axis and c-axis of t-ZrO2 is noticed with respect to the enhanced Zn2+/Fe3+ additions. The lattice data of ZnFe2O4 displayed negligible deviations as a function of incremental Zn2+/Fe3+ additions. The crystallite size data of both t-ZrO2 and ZnFe2O4 structures deliberated an obvious surge with respect to the increments in heat treatment.

Journal Pre-proof 3.4

X-ray photoelectron spectroscopy

XPS data unveiled the overall elemental composition and chemical states of constituent elements in the investigated systems. The overall spectra and the core-level spectra of individual (Fe, Zn, O, Y, Zr) elements are illustrated in Figures 4a-f. Fe 2p core level spectra (Figure 4b) revealed two peaks that are resolved in two doublets at 711.2, 712.2, 724.1 and 726 eV respectively and the shakeup satellite  719 eV authenticated the existence of Fe3+ state. An increase in binding energy of Fe 2p3/2 in ZnFe2O4 when compared to Fe2O3, is attributed due to

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the different oxygen environment of Fe3+ when exposed to Zn2+ [58–60]. The high resolution

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spectra of zinc (Figure 4c) exhibited the binding energy of Zn 2p3/2 at 1021.3 eV, which is

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attributed to Zn2+ where the cation occupies the tetrahedral site of spinel structure[61]. The O 1s

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spectra (Figure 4d) is deconvoluted into two Gaussian fits corresponding to the binding energies of Zr-O and Zn-O respectively. The core level energy spectra of Y 3d (Figure 4e) exhibited

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signals at 156.7 and 159 eV confined to Y3+ while the Zr4+ chemical states is ensured from the

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Zr 3d (Figure 4f) signals exhibited at 181.6 and 184 eV. The minor shift in binding energy observed in the spectra is due to the charge imbalance that is created by the Y3+ accommodation

3.5

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at the ZrO2 lattice sites [62–68].

Morphological and mechanical features

The microstructure of the selective sintered specimens (Figure 5) elucidated pore-free morphological features. A clear distinction of two different grains that correspond to t-ZrO2 and ZnFe2O4 were elucidated from the microstructures. The micrograph of other compositions (Supporting Information S4) inclusive of pure ZrO2 also elucidate the presence of pore free microstructures and in specific the morphologies of 10ZFZ, 20ZFZ and 60ZFZ revealed two different grains, which confirm the formation of composite mixtures. The impregnation of ZnFe2O4 grains in the dense ZrO2 matrix is apparent and this inference has also been verified from the elemental mapping results. Elemental mapping (Figure 6 and 7) revealed a collective

Journal Pre-proof distribution of constituent elements and their existence in the bulk of the specimen. Crystallization of ZnFe2O4 grains with inconsequential variations in their size is apparent throughout the t-ZrO2 matrix in case of 40ZFZ while the crystallization of ZnFe2O4 is irregular alongside with their higher size enunciated in 100ZFZ. Moreover, the minimum level of Zn2+/Fe3+ occupancy in t-ZrO2 as stated in quantitative X-ray analysis is also emulated in elemental mapping that ensure their limited dispersion in ZrO2 matrix. On the contrast, the evidence of Zr4+ occupancy at the ZnFe2O4 matrix is discarded from the elemental mapping

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results.

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The load vs. depth profiles obtained from the indentation and their corresponding mechanical data is presented in Table 4 and Figure 8. A smooth loading and unloading segments determined

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from the indentation profiles justify the good compaction and close packing of grains in the

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specimen. The indentation data of 8YSZ is also presented in the Table 4 for comparative

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purpose. Minor variations in mechanical data has been derived from the nanoindentation, despite the assorted range of phase compositions determined from the quantitative analysis. The

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Young’s modulus and hardness data of 10ZFZ and 20ZFZ displayed relatively minimum values

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among the compositions due to the presence of m-ZrO2 trace in this particular system. Furthermore, crystallization of ZnFe2O4 alongside the major t-ZrO2 component unveiled a marginal increment in the mechanical data of 40ZFZ. Nevertheless, the mechanical data of 100ZFZ that possessed -Fe2O3 as a tertiary phase in minor amount exhibited negligible change on comparison with the other specimens.

3.6

Magnetic properties

The magnetization curves (Figure 9) and the resultant data (Table 4) unveiled a significant trend that demonstrated a good coherence with the corresponding phase composition of the investigated systems. Magnetization values displayed gradual increment in the order of 10ZFZ,

Journal Pre-proof 20ZFZ, 40ZFZ, 60ZFZ and 100ZFZ. The attained result is a good indication on the role of ZnFe2O4 to unveil enhanced magnetic features. All the investigated systems intend to display ferrimagnetic features that are mainly complemented from the substantial presence of ZnFe2O4 component in the composite mixtures. The strong ferrimagnetic features of ZnFe2O4 is well established from the previous investigations [69].

3.7

In vitro analysis

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Quantification of the number of viable cells has been attained through in vitro cell viability

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assay of MG-63 cell lines (Figure 10). Results confirmed negligible toxicity in all the

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compositions and established good corroboration with that of control. Even the highest

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concentration of 1000 µg/ml revealed cell viability of  96 % that validate the marginal toxicity of resultant specimen. While, MG-132 cells displayed a considerable reduction in the cell

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viability. Phase contrast images (Figure 11) portray enhanced cell proliferation of MG-63 cell

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lines (500 g/ml) for all the different combinations similar to PBS control. Further, the fluorescence images (Figure 12) also validated the maximum cell sustainability under the

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exposure of sample at different concentrations. Uniform green color in the micrographs

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demonstrated improved viability of cells and negligible dead cells (red color). Osteoblast proliferation has been evaluated through ALP enzyme release and osteogenic potential of MG63 cells in the specimen were measured using qRT-PCR and their corresponding agarose gel images are presented in Figure 13. Uniform band intensities were determined in agarose images of composite specimen, which established a good consistency with the control.

4.

Discussion

The overall study unveiled the influence of Zn2+/Fe3+ to facilitate the crystallization of ZnFe2O4 in ZrO2 matrix. 10ZFZ and 20ZFZ retain t-ZrO2 at room temperature along with the associated t-  m-ZrO2 degradation as determined from the quantitative analysis. While, the structural

Journal Pre-proof stability of t-ZrO2 is achieved when Zn2+/Fe3+ content is enhanced to 40 mol. % alongside the crystallization of ZnFe2O4. Furthermore, t-ZrO2 matrix plays a pivotal role to retain ZnFe2O4 until 1300 °C. It is noteworthy to mention that all the synthesis were performed with equimolar concentrations of Zn2+/Fe3+ in the ZrO2 system. Nevertheless, 10ZFZ and 20ZFZ ensured the formation of t-ZrO2 and ZnFe2O4 mixtures alongside the minor trace of m-ZrO2. Zn2+/Fe3+ combine in the range of 40 - 100 mol. % witnessed the enhanced crystallization of ZnFe2O4 as a secondary component alongside t-ZrO2. The incidence of α-Fe2O3 crystallization as a tertiary

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component in case of 60ZFZ and 100ZFZ ensured the presence of excess Fe3+ in these systems

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to enhance its oxidation behavior.

t-  m-ZrO2 degradation witnessed in the systems are influenced by two factors namely the

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concentration changes in Zn2+/Fe3+ and heat treatment temperature. It has also been witnessed

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that this degradation displayed a reverse trend of m-  t-ZrO2 with incremental heat treatments.

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In specific, this t-  m-ZrO2 transition is facilitated by Fe3+ rather than the presence of Zn2+ in the system. This particular inference is attained with the aid of individual substitutions, where

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m-ZrO2 is witnessed in Fe3+ only substitutions rather than the Zn2+ only substitutions in 8YSZ.

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Further, Fe3+ prefers to displace Y3+ from ZrO2 and hence YFeO3 has been witnessed and also the reverse m-  t-ZrO2 transition with respect to the temperature increments is determined in Fe3+ only system. While the limited occupancy of Zn2+ at ZrO2 lattice has led to the discrete crystallization of ZnO as witnessed in Zn2+ only substitution. Nevertheless, the individual substitutions of Zn2+ and Fe3+ favor their limited accommodation at the ZrO2 lattice site, which is concentration and temperature dependent effect. Hence, the dual occupancy of Zn2+/Fe3+ at the tZrO2 lattice sites is highly plausible. Moreover, the

elemental mapping results and the

significant contraction of lattice parameters of t-ZrO2 on comparison with the standard 8YSZ also confirms this dual occupancy of Zn2+/Fe3+. The saturation limit of Zn2+/Fe3+ occupancy at tZrO2 lattice is attained in 10ZFZ and consequently the excess Zn2+/Fe3+ in system crystallizes as

Journal Pre-proof ZnFe2O4 and this trend is obvious as enhanced phase yield of ZnFe2O4 is witnessed as a function of Zn2+/Fe3+ additions.

The observed decline in the lattice data of t-ZrO2 is mainly due to the possible occupancy of lower sized Zn2+ (0.74 Å) and Fe3+ (0.64 Å) for the higher sized Y3+ (1.019 Å) stabilized t-ZrO2 lattice sites. It is noteworthy to mention that the substantial amount of lower sized Zn2+/Fe3+ occupancy ensured a considerable decline in the lattice data of t-ZrO2 and this is emulated in the

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 2 wt. % of ZnFe2O4 detected in 10ZFZ. Further, a marginal increment in  5 wt.% of ZnFe2O4

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in 20ZFZ thus emphasize the attainment of saturation limit in the Zn2+/Fe3+ occupancy at t-ZrO2

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lattice. A sharp increment in the ZnFe2O4 phase content is noticed from 40ZFZ alongside tZrO2; nonetheless, with the detection of -Fe2O3 trace in 60ZFZ and 100ZFZ. This

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crystallization of additional -Fe2O3 is mainly attributed to the excess occupancy and affinity of

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Zn2+ rather than the inclination of Fe3+ towards t-ZrO2 lattice. The plausible Zn2+ attraction

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towards Zr4+ is accomplished by the comparably minor size difference between Zr 4+ (0.72 Å) and Zn2+ (0.74 Å) rather than the Zr4+ and Fe3+ (0.64 Å), which tends to agree with the basic

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rules on the formation of solid solution.

The mechanical data of stoichiometric ZnFe2O4 envisaged values in the analogous manner. The presence of ZnFe2O4 in the composite system has not been found detrimental in the resultant mechanical properties and these values exhibited good coherence with the pure t-ZrO2 stabilized system. The mechanical data also exhibited good consistency with the already well-established commercial ZrO2 products [70,71]. On the other hand, the dominant role of ZnFe2O4 is evident as the ferrimagnetic features are displayed by the composite system. In vitro cytotoxicity assays ensured negligible toxicity and improved cell proliferation for all the tested specimens that validates the superior biocompatibility of the composite system.

Journal Pre-proof 5.

Conclusion

The overall investigation revealed the potential to yield t-ZrO2/ZnFe2O4 composites through a simple aqueous sol-gel synthetic approach. A wide range of composite mixtures have been attained with the dominant phase composition comprising t-ZrO2 and ZnFe2O4. The combined occupancy of Zn2+/Fe3+ in ZrO2 lattice have been determined and moreover this composite system revealed a reverse m-  t-ZrO2 transition that were mainly contributed by the factors of Zn2+/Fe3+ content and temperature gradient. 20 mol.% each of Zn2+ and Fe3+ additions in ZrO2

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has led to the formation of t-ZrO2/ZnFe2O4 composite mixtures at 1300 °C devoid of additional

ementary phases of m-ZrO2 and -Fe2O3 in trace amounts. The better

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% prefer to yield

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phases. While the concentrations of Zn2+ and Fe3+ below and above this specific limit of 20 mol.

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mechanical and magnetic features displayed by these t-ZrO2/ZnFe2O4 composite is also evident from the investigation. Moreover, the good biocompatibility and non-toxic behavior of the

6.

Acknowledgement

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composite system is evident from the in vitro studies.

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The financial assistance received from Council of Scientific and Industrial Research (CSIR)

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[Reference: 01(2952)/18/EMR-II dated 01.05.2018] India is acknowledged. The facilities availed from Central Instrumentation Facility (CIF) of Pondicherry University is also acknowledged. Subina Raveendran acknowledges CSIR, India (Ref. No. 09/559/0122/18-EMR1 dated 26/04/2018) for Senior Research Fellowship. The characterization facilities availed from IIT Bombay under INUP which is sponsored by DeitY, MCIT, Government of India are gratefully acknowledged.

Journal Pre-proof 7. [1]

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Journal Pre-proof List of Tables

Precursor concentrations along with their sample codes ZrOCl2

Y(NO3)3

Fe(NO3)3

Zn(NO3)2

8YSZ

0.50

0.04

-

-

10ZFZ

0.50

0.04

0.025

0.025

20ZFZ

0.50

0.04

0.050

0.050

40ZFZ

0.50

0.04

0.100

0.100

60ZFZ

0.50

0.04

0.150

0.150

100ZFZ

0.50

0.04

0.250

0.250

10ZZ

0.50

0.04

-

0.050

100ZZ

0.50

0.04

10FZ

0.50

0.04

100FZ

0.50

0.04

-

0.500

0.050

-

ro

of

Sample code

-

0.500

-p

Table 1

Phase content and crystallite size determined from the refinement of five

re

Table 2

different compositions heat treated at 900, 1100 and 1300 °C. Phase Fraction (Wt%) m-ZrO2

ZnFe2O4 900°C

α- Fe2O3

t-ZrO2

ZnFe2O4

03.11 (3)

-

47

116

43.71 (1)

03.69 (2)

-

48

113

43.73 (2)

08.76 (2)

-

46

104

35.98 (1)

06.85 (2)

07.33 (2)

39

114

12.44 (3)

04.62 (3)

48

129

t-ZrO2 10ZFZ

49.17 (2) 52.58 (3)

40ZFZ

47.49 (2)

60ZFZ

49.87 (3)

10ZFZ 20ZFZ 40ZFZ 60ZFZ 100ZFZ 8YSZ 10ZFZ 20ZFZ 40ZFZ 60ZFZ 100ZFZ

56.03 (2)

Jo

100ZFZ

47.70 (2)

ur

20ZFZ

Crystalline size (nm)

na

lP

Sample Code

61.04 (2)

26.89 (2)

35.63 (3)

1100°C 03.31 (2)

-

69

90

126

140

57.01 (2)

36.70 (2)

03.97 (3)

02.30 (3)

56.85 (3)

33.04 (3)

06.48 (2)

03.61 (2)

123

213

55.98 (2)

28.79 (1)

05.87 (2)

09.33 (3)

120

247

12.36 (2) 1300°C

08.33 (2)

117

357

127

228

176

313

181

405

183

432

196

457

45.76 (2)

100.00 (0) 90.70 (2) 89.80 (3) 84.90 (2) 81.50 (4) 68.40 (4)

33.53 (2)

7.30 (3) 4.80 (2) -

2.00 (2) 5.40 (2) 15.10 (3) 16.00 (4) 25.00 (1)

2.50 (2) 6.60 (1)

Journal Pre-proof Table 3

Rietveld agreement factors and lattice parameters determined from the refinement of five different ZFZ compositions heat treated at 900, 1100 and 1300 °C 900 °C

Sample

Lattice Parameters (Å)

t-ZrO2

Code

m-ZrO2

ZnFe2O4

c- axis 5.1722 (2) 5.1571 (1) 5.1511 (3) 5.1537 (1) 5.1520 (3) 5.1458 (2)

a-axis 5.1487(1) 5.1475 (3) 5.1480 (2) 5.1478 (3) 5.1485 (2)

b-axis 5.1974 (3) 5.1994 (1) 5.1978 (2) 5.1999 (3) 5.2045 (2)

c-axis 5.3212 (2) 5.3202 (3) 5.3180 (2) 5.3250 (4) 5.3156 (2)

a=b=c- axis

YSZ 10ZFZ 20ZFZ 40ZFZ 60ZFZ 100ZFZ

a=b-axis 3.7063 (6) 3.6351 (3) 3.6329 (2) 3.6339 (1) 3.6286 (1) 3.6264 (2)

10ZFZ 20ZFZ 40ZFZ 60ZFZ 100ZFZ

3.6328 (2) 3.6327 (3) 3.6345 (1) 3.6321 (3) 3.6331 (2)

5.1443 (4) 5.1444 (3) 5.1390 (2) 5.1395 (2) 5.1422 (2)

5.1498 (4) 5.1497 (3) 5.1483 (2) 5.1475 (3) 5.1485 (2)

5.1882 (3) 5.1881 (1) 5.1943 (2) 5.1886 (3) 5.1948 (2)

5.3284 (2) 5.3283 (3) 5.3253 (4) 5.3239 (2) 5.3222 (3)

8.4391 (3) 8.4416 (2) 8.4363 (2) 8.4414 (3) .8.4416 (3)

10ZFZ 20ZFZ 40ZFZ 60ZFZ 100ZFZ

3.6273 (3) 3.6264 (2) 3.6269 (3) 3.6263 (4) 3.6269 (2)

5.1284 (3) 5.1271 (3) 5.1263 (2) 5.1260 (4) 5.1261 (5)

5.1471 (2) 5.1491 (3) -

5.1902 (3) 5.1839 (4) -

5.3154 (2) 5.3120 (3) -

8.4286 (6) 8.4264 (2) 8.4340 (3) 8.4302 (4) 8.4332 (2)

Rietveld agreement factors

a=b- axis 5.0534 (2) 5.0406 (3) 1100 °C 5.0429 (1) 5.0354 (2) 5.0375 (4) 5.0395 (3) 1300 °C 5.0418 (3) 5.0416 (2)

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RBragg 07.12 04.69 05.98 05.99 05.66 07.25

13.7552 (2) 13.7443 (3) 13.7487 (2) 13.7420 (1)

1.10 1.14 1.17 1.19 1.04

07.26 06.87 07.53 08.80 07.38

1.98 1.79 1.56 1.52 1.22

7.52 6.66 6.58 7.82 7.90

13.7584 (2) 13.7440 (4)

Table 4

lP

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13.7454 (3) 13.7452 (2)

2 1.55 1.02 1.03 0.90 0.76 1.04

c- axis

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8.4343 (1) 8.4382 (2) 8.4382 (3) 8.4378 (2) 8.4349 (3)

α-Fe2O3

Mechanical properties derived from the indentation and magnetic properties of

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assorted range of Zn2+ and Fe3+ additions in 8 mol.% Y2O3 stabilized ZrO2 system Young’s

modulus

Hardness (GPa)

Magnetic Coercivity (Oe)

Magnetization

13.29 ± 1.57

140.90

14.55 ± 1.12

135.60

0.560 (emu/g) 1.440

186.92 ± 7.08

15.86 ± 1.17

132.70

1.460

60ZFZ

184. 88± 10.11

15.009 ± 0.51

161.60

1.845

100ZFZ

187.42 ± 7.07

14.91 ± 1.12

95.50

2.350

8YSZ

170.54 ± 5.07

12.06 ± 0.24

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20ZFZ 40ZFZ

170.033 ± 7.03 (GPa) 178.88 ± 8.75

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10ZFZ

Mechanical

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Sample Code

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XRD patterns for five different Zn2+/Fe3+ substituted ZrO2 compositions recorded

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after different heat treatment temperatures (900, 1100 and 1300 °C )

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Figure 1

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List of Figures

Raman spectra for five different Zn2+/Fe3+ substituted ZrO2 compositions

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recorded after heat treatment at 900 (a), 1100 (b) and 1300 °C (c). The symbols t,

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m, ZF and H respectively denotes for t-ZrO2, m-ZrO2, ZnFe2O4 and α-Fe2O3.

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Figure 2

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Refined X-ray diffraction patterns of selective compositions. Figs. 3a, 3band 3c corresponds to 10ZFZ, 40ZFZ and 100ZFZ heat treated at 1300 °C. 10ZFZ

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display t-ZrO2 along with minor m-ZrO2 content. 40ZFZ displays the combination of t-ZrO2 and ZnFe2O4 whereas an excess of -Fe2O3 is determined

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in 100ZFZ.

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Figure 3

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XPS spectrum for the selective t-ZrO2/ ZnFe2O4 composite heat treated at 1300 °C. Figure 4a represents the overall survey spectra of 40ZFZ composition. The

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Figure 4

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individual core level spectrum of Fe 2p, Zn 2p, O 1s, Y 3d and Zr 3d are respectively displayed in Figures 4b, c, d, e and f.

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Field emission scanning electron microscopy (FE-SEM) images of the selective

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Figure 5

t-ZrO2/ZnFe2O4 composites after heat treatment at 1300 °C. Figures 5a and b

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respectively corresponds to 40ZFZ and 100ZFZ.

Elemental mapping of 40ZFZ after heat treatment at 1300 °C.

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Elemental mapping of 100ZFZ after heat treatment at 1300 °C.

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Figure 6

Figure 8

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Indentation profiles of five different Zn2+/Fe3+ combination in ZrO2 system and pure 8YSZ at 1300 °C.

Hysteresis curves derived from the VSM analysis of a assorted range of Zn2+ and

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Fe3+ additions in 8 mol.% Y2O3 stabilized ZrO2 system at 1300 °C.

Figure 10

Cell viability of PBS (control) and five different ZnFe2O4/ZrO2 composite powders heat treated at 1300 °C.

Optical microscopic images of MG-63 cells cultured with PBS and five different

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ZnFe2O4/ZrO2 composite specimens.

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Fluorescence micrographs of live/dead dye-stained MG-63 cells incubated with ZnFe2O4/ZrO2 composite specimens.

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(a) Relative ALP expression in MG-63 cells treated with selective ZnFe2O4/ZrO2

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composite specimens determined by qRT PCR (b) Agarose gel image of qRT-

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PCR products.

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Figure 13

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Research Highlights

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In situ formation of ZrO2/ZnFe2O4 composites with assorted composition ratios.

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Zn2+/Fe3+ dependent evolution of monoclinic ZrO2 at low temperatures.

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Gradual monoclinic to tetragonal ZrO2 transition dependent upon Zn2+/Fe3+ content and progressive heat treatments.

Better mechanical and in vitro compatibility displayed by ZrO2/ZnFe2O4 composites.

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Magnetic features determined by the ZnFe2O4 content in composites

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