Effects of Mg doping on the properties of highly transparent conductive and near infrared reflective Zn1−xMgxO:Ga films

Highly transparent conductive and near infrared (IR) reflective Gallium-doped ZnMgO (Zn_1−xMg_xO:Ga) films with Mg content from 0 to 10 at% were deposited on glass substrate by DC reactive magnetron sputtering. X-ray diffraction shows all the ZnMgO:Ga films are polycrystalline and have wurtzite structure with a preferential c-axis orientation. Hall measurements indicate that the resistivity of these films obviously increases with the Mg concentration increasing. The average transmittance of Zn_1−xMg_xO:Ga films is over 90% in the visible range. All the Zn_1−xMg_xO:Ga films have low transmittance and high reflectance in the IR region.     

Structural and P NMR investigation of Bi(MM′)2PO6 statistic solid solutions: Deconvolution of lattice constraints and cationic influences

Two solid solutions BiM_xMg_(2−x)PO₆ (with M²⁺=Zn or Cd) have been studied through ³¹P MAS NMR. The analysis has been performed on the basis of refined crystal structures through X-ray diffraction and neutron diffraction. The BiZn_xMg_(2−x)PO₆ does not provide direct evidence for sensitive changes in the phosphorus local symmetry. This result is in good agreement with structural data which show nearly unchanged lattices and atomic separations through the Zn²⁺ for Mg²⁺ substitution. On the other hand, the Cd²⁺ for Mg²⁺ substitution behaves differently. Indeed, up to five resonances are observed, each corresponding to one of the five first-cationic neighbour distributions, i.e. 4Mg/0Cd, 3Mg/1Cd, 2Mg/2Cd, 1Mg/3Cd and 0Mg/4Cd. Their intensities match rather well the expected weight for each configuration of the statistical Cd²⁺/Mg²⁺ mixed occupancy. The match is further improved when one takes into account the influence of the 2nd cationic sphere that is available from high-field NMR data (18.8 T). Finally, the fine examination of the chemical shift for each resonance versus x allows to de-convolute the mean Z/a² effective field into two sub-effects: a lattice constraint-only term and a chemical-only term whose effects are directly quantifiable.     

Fabrication and Optical Properties of Aligned Zn1-xMgxO Nanowire Arrays

Aligned Zn_1-xMg_xO nanowire arrays were successfully prepared on Si(111) substrates via the chemical vapor deposition (CVD) method with a mixture of ZnO, Mg, and activated carbon powders as reactants. The microstructures and optical properties of the synthesized Zn_1-xMg_xO nanowire arrays were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis X-ray (EDAX), and photoluminescence (PL) spectrum analytic apparatus, respectively. While Mg content was achieved or less approximately 0.29 (x, atomic ratio) in ZnO lattice, the crystal lattice of the synthesized samples exhibited wurtzite structure. The Mg atoms were distributed into the ZnO crystal as the interstitial and displaced atoms, and there was no phase separation in preparing Zn_1-xMg_xO nanowire arrays. However, as the Mg content was up to 0.53 (x) in the fabricated Zn_1-xMg_xO samples, a clear phase separation phenomena appeared in the Zn_1-xMg_xO crystal. Compared with the PL spectrum of the pure ZnO nanowire arrays, the analytic results showed that a blue-shift of the near-band edge emission with increasing Mg content was observed in the Zn_1-xMg_xO arrays. And the relative intensities of green peak at ca 535 nm and UV emission peak at ca 376 nm were all restrained.     

Effect of composition on structural and magnetic properties of nanocrystalline Ni0.8−xZn0.2MgxFe2O4 ferrite

Nanocrystalline magnetic particles of Ni_0.8−xZn_0.2Mg_xFe₂O₄ ferrites with x lying between 0.0 and 0.8 were synthesized using metal nitrates and freshly extracted egg-white. The synthesized powders were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and transmission electron microscopy (TEM). With increasing magnesium concentration, the lattice constant increases while X-ray density decreases. The average crystallite size determined from XRD data using Scherrer formula lie in the range of 35–59 nm. TEM image shows spherically agglomerated particles with average crystallite size agreed well with that obtained from XRD. Magnetic properties measured at room temperature by vibrating sample magnetometer (VSM) reveal a decrease in saturation magnetization up to Mg content of 0.6. In agreement with FT-IR results, the unexpected increase in the magnetization at Mg content of 0.8 can be attributed to the tendency of Mg²⁺ ions to occupy the tetrahedral site. The decrease in the value of coercivity with increasing magnesium content can be explained based on the magneto-crystalline anisotropy.     

Consequence of doping mediated strain and the activation energy on the structural and optical properties of ZnO:Cr nanoparticles

We report on the sol-gel synthesis of Zn_1−xCr_xO (x=0.0, 0.05, 0.10, 0.15 and 0.20) nanoparticles. These nanoparticles were characterized by using thermogravimetry/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman and Photoluminescence (PL). Electronegativity of Cr ions (Cr³⁺) reduces the final decomposition temperature by 40 °C and activation energy of the reaction when Cr is doped into ZnO. Doping of higher Cr concentration (x≥0.10) into ZnO shows formation of secondary spinel (ZnCr₂O₄) phase along with the hexagonal (ZnO) and is revealed by XRD. Formation of secondary phase changes the activation energy of the reaction and thus the strain in ZnO lattice. In Raman spectra, additional Raman modes have been observed for Zn_1−xCr_xO nanoparticles, which can be assigned to the modes generated due to Cr doping. The Cr doping into ZnO is also supported by PL, in which vacancies are formed with Cr ion incorporation and emission band shifts towards higher wavelength.     

Effects of gold catalysts and thermal evaporation method modifications on the growth process of Zn1−xMgxO nanowires

In this paper, we investigate the roles of gold catalysts and thermal evaporation method modifications in the growth process of Zn_1−xMg_xO nanowires. Zn_1−xMg_xO nanowires are fabricated on silicon substrates with and without using a gold catalyst. Characterizations reveal that Mg acts in a self-catalyst role during the growth process of Zn_1−xMg_xO nanowires grown on catalyst-free substrate. The optical properties and crystalline quality of the Zn_1−xMg_xO nanowires are characterized by room temperature photoluminescence (PL) measurements and Raman spectroscopy, respectively. The Raman and PL studies demonstrate that the Zn_1−xMg_xO nanowires grown using the catalyst-free method have good crystallinity with excellent optical properties and have a larger band-gap in comparison to those grown with the assistance of gold.     

Effect of Mg doping on morphology,photocatalytic activity and related biological properties of Zn1−xMgxO nanoparticles

The objective of this study is to synthesize ZnO and Mg doped ZnO (Zn_1−xMg_xO) nanoparticles via the sol-gel method, and characterize their structures and to investigate their biological properties such as antibacterial activity and hemolytic potential.Nanoparticles (NPs) were synthesized by the sol-gel method using zinc acetate dihydrate (Zn(CH₃COO)₂.2H₂O) and magnesium acetate tetrahydrate (Mg(CH₃COO)₂.4H₂O) as precursors. Methanol and monoethanolamine were used as solvent and sol stabilizer, respectively. Structural and morphological characterizations of Zn_1−xMg_xO nanoparticles were studied by using XRD and SEM-EDX, respectively. Photocatalytic activities of ZnO and selected Mg-doped ZnO (Zn_1−xMg_xO) nanoparticles were investigated by degradation of methylene blue (MeB). Results indicated that Mg doping (both 10% and 30%) to the ZnO nanoparticles enhanced the photocatalytic activity and a little amount of Zn0.90 Mg0.10 O photocatalyst (1.0 mg/mL) degraded MeB with 99% efficiency after 24 h of irradiation under ambient visible light. Antibacterial activity of nanoparticles versus Escherichia coli ( E. coli ) was determined by the standard plate count method. Hemolytic activities of the NPs were studied by hemolysis tests using human erythrocytes. XRD data proved that the average particle size of nanoparticles was around 30 nm. Moreover, the XRD results indicatedthat the patterns of Mg doped ZnO nanoparticles related to ZnO hexagonal wurtzite structure had no secondary phase for x ≤ 0.2 concentration. For 0 ≤ x ≤ 0.02, NPs showed a concentration dependent antibacterial activity against E. coli . While Zn_0.90Mg_0.10 O totally inhibited the growth of E. coli , upper and lower dopant concentrations did not show antibacterial activity.     

Cation distribution in MgxZn1 − x(HCOO)2·2H2O mixed crystals: X-ray diffraction and double matrix infrared spectroscopy

The metal ion distributions at the two metal sites (hexaformate-coordinated Me1 sites and mixed-coordinated Me2 sites) in the title mixed crystals as determined by single crystal X-ray diffraction and double matrix infrared spectroscopic methods are presented and discussed. The mixed formates are isostructural with the end compounds (space group P2₁/c). The local metal ion concentrations as a function of the total metal ion concentrations exhibit a clear preference of Zn²⁺ ions to Me1 sites and the Mg²⁺ ions to Me2 sites.The analysis of the infrared spectra reveals that the spectral regions 2300–2500 cm⁻¹ (ν_OD of matrix-isolated HDO molecules) and 1300–1400 cm⁻¹ (symmetric COO stretching (ν₂) and bending CH (ν₅) modes) are mostly sensitive to the metal ion environment. The inclusion of Mg²⁺ and Zn²⁺ in the structures of Zn(HCOO)₂·2H₂O and Mg(HCOO)₂·2H₂O, respectively, leads to an appearance of new infrared bands corresponding to ν_OD of HDO molecules bonded to the incorporated ions (i.e. new hydrogen bonding systems MgOH₂⋯OCHOZn and ZnOH₂⋯OCHOMg are formed in the mixed formates). The respective new bands are observed at small concentrations of included Mg²⁺ ions (about 5 mol%, x = 0.05) and at considerably higher concentrations of included Zn²⁺ ions (about 30 mol%, x = 0.7). Contrarily, the ν₂ and ν₅ modes caused by the incorporated cations bonded to formate ions occur at x ≥ 0.3 and x ≤ 0.85 (Mg²⁺ ions in Zn(HCOO)₂·2H₂O and Zn²⁺ ions in Mg(HCOO)₂·2H₂O, respectively). Thus, the infrared spectroscopy experiments confirm the single crystal X-ray measurements that the Mg²⁺ ions are localized predominantly at Me2 sites and the Zn²⁺ ions at Me1 sites in the title mixed crystals. The pronounced preference of the Mg²⁺ ions to Me2 sites is owing to the strong affinity of these ions to water molecules.     

Effect of annealing temperature on the structural and optical properties of Zn1−xMgxO particles prepared by oxalate precursor

Zn_1−xMg_xO particles were prepared using zinc and magnesium oxalate precursor by co-precipitated method. The lattice constants of Zn_1−xMg_xO proved that the interstitial Mg formed at 500 °C and Mg replaced Zn in ZnO tetrahedral coordination at 800 °C. Compared with the ZnO, the absorbing band edge of the Zn_1−xMg_xO displayed blue shifts. The room temperature photoluminescence was similar to ZnO and variation of Mg content did not change the shape or peak position of the emission spectra markedly when it was annealed at 500 °C. However, its blue emission band disappeared, and a relatively strong green light emission at 498 nm appeared after annealed at 800 °C. The photoluminescence intensity ratios I_(green)/I_(UV) of Zn_1−xMg_xO varied with Mg content and the green light emission peak shifted from 498 nm to 472 nm when Mg content increased from 0 to 2.0 at.%.     

Structural and physical properties of Mg3−xZnxSb2 (x=0-1.34)

The Mg_3−xZn_xSb₂ phases with x=0-1.34 were prepared by direct reactions of the elements in tantalum tubes. According to the X-ray single crystal and powder diffraction, the Mg_3−xZn_xSb₂ phases crystallize in the same P3¯m1 space group as the parent Mg₃Sb₂ phase. The Mg_3−xZn_xSb₂ structure is different from the other substituted structures of Mg₃Sb₂, such as (Ca, Sr, Ba) Mg₂Sb₂ or Mg_5.23Sm_0.77Sb₄, in a way that in Mg_3−xZn_xSb₂ the Mg atoms on the tetrahedral sites are replaced, while in the other structures Mg on the octahedral sites is replaced. Thermoelectric performance for the two members of the series, Mg₃Sb₂ and Mg_2.36Zn_0.64Sb₂, was evaluated from low to room temperatures through resistivity, Seebeck coefficient and thermal conductivity measurements. In contrast to Mg₃Sb₂ which is a semiconductor, Mg_2.36Zn_0.64Sb₂ is metallic and exhibits an 18-times larger dimensionless figure-of-merit, ZT, at room temperature. However, thermoelectric performance of Mg_2.36Zn_0.64Sb₂ is still poor and it is mostly due to its large electrical resistivity.     

Structural and magnetic properties of the Zn0.8−4xHoxOy (0.05 ≤ x ≤ 0.10) compounds prepared by solid state reactions

Zn_0.8−4xHo_xO_y (0.05 ≤ x ≤ 0.10) diluted magnetic semiconductors were prepared by the solid state reaction method. We have studied the structural properties of the samples by using the XRD, SEM, and EDX techniques. The SEM results clearly demonstrate that Ho³⁺ ions are quite well substituted for Zn²⁺ in the ZnO lattice, and the grains of the samples are very well connected to each other and tightly packed. From the XRD and EDX spectra of the samples, it has been concluded that the substitution of Ho causes no change in the hexagonal wurtzite structure of ZnO. According to our M–H and M–T measurements paramagnetism has been observed for all the samples from our attainable lowest temperature of 10 K to 300 K. Furthermore, the trend of the AC-susceptibility (χ) versus temperature curves, measured under an AC-magnetic field of 10 Oe, also support our conclusion about the paramagnetic contribution in the Zn_0.8−4xHo_xO_y compounds explored in this study. In order to clearly see the paramagnetic contribution, and whether there is also a ferromagnetic or antiferromagnetic contribution or not the inverse susceptibility (1/χ) against temperature curves are also plotted. Those curves indicate that, the substitution of Ho into the ZnO compound causes, in addition to the paramagnetism, a weaker antiferromagnetic (AFM) interaction.     

Magnesium doping on brownmillerite Ca2FeAlO5

Ca₂FeAl_1−xMg_xO₅ (x=0, 0.05 and 0.1) compounds adopting the brownmillerite-type structure were prepared by a self-combustion route using two different fuels. Characterisation was performed using X-ray powder diffraction, Mössbauer spectroscopy, magnetisation measurements, chemical analysis, scanning electron microscopy and 4-point dc conductivity measurements. Global results indicate that the solubility limit was reached for x=0.1. An antiferromagnetic behaviour was detected for all studied compositions, with magnetic ordering temperatures of 340 and 290 K for x=0 and 0.05, respectively. Mg doping increases the number of iron cations in tetrahedral sites, which induces magnetisation enhancement at low temperatures through the coupling between octahedral iron cations in different octahedral planes. The compounds exhibit semiconductor behaviour and Mg²⁺ doping yields a significant enhancement of the total conductivity, which can be essentially attributed to the presence of Fe⁴⁺ ions.     

One-dimensional NiCuZn ferrite nanostructures: Fabrication, structure, and magnetic properties

Ni_0.5−xCu_xZn_0.5Fe₂O₄ (0.0≤x≤0.5) ferrite nanofibers with diameters of 80-160 nm have been prepared by electrospinning and subsequent heat treatment. Both the average grain size and lattice parameter are found to increase with the addition of copper. Fourier transform infrared spectra indicate that the portion of Fe³⁺ ions at the tetrahedral sites move to the octahedral sites as some of the substituted Cu²⁺ ions get into the tetrahedral sites. Vibrating sample magnetometer measurements show that the coercivity of these ferrite nanofibers decreases with increasing Cu concentration, whereas the specific saturation magnetization initially increases, reaches a maximum value at x=0.2 and then decreases with the Cu content further increase. Notable differences in magnetic properties at room temperature (298 K) and 77 K for the Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ nanofibers and corresponding powders are observed and mainly arise from the grain size and morphological variations between these two materials.     

K2Mg5−xSn3 and K3Mg18Tt11 (Tt=Sn, pb) with two types of Mg-Sn/Pb frameworks

K₂Mg_5−xSn₃ (x=0.28) and K₃Mg₁₈Tt₁₁ (Tt=Sn, Pb) have been synthesized by reacting the mixture of the corresponding pure elements at high temperature, and structurally characterized by single-crystal X-ray diffraction studies. K₂Mg_5−xSn₃ (x=0.28) is isostructural with Ni_7−xSbQ₂ (Q=Se, Te) series and features 2D corrugated [Mg_5−xSn₃] layers that are separated by K⁺ cations. The structure of K₃Mg₁₈Tt₁₁ (Tt=Sn, Pb) is closely related to the Ho₂Rh₁₂As₇ structural type and features 3D [Mg₁₈Tt₁₁] framework composed of 1D [Mg₁₈Tt₁₁] columns that are interconnected via Mg-Tt bonds, forming 1D hexagonal tunnels occupied by the K+ cations. Electronic structure calculations indicate that Mg atoms can function as either electron donor or as a participator in the network along with Tt atoms. Magnetic property measurements and band structure calculations indicate that these compounds are metallic.     

Formation, sintering, and electrical conductivity of perovskite Sm(Cr1−xMgx)O3 (0?x?0.23) prepared by the hydrazine method

The presence of SmCrO₄ is experimentally established. In Mg²⁺-substituted SmCrO₃, single-phase perovskite Sm(Cr_1−xMg_x)O₃, where x=0-0.23, are formed at ∼830°C by decomposition of Sm(Cr_1−xMg_x)O₄ which crystallizes at 530-570°C from amorphous materials prepared by the hydrazine method. Sm(Cr_1−xMg_x)O₃ solid solution powders consisting of submicrometer-size particles are sinterable; dense materials can be fabricated by sintering for 2 h at 1700°C in air. The relative densities, grain sizes, and electrical conductivities increase with increased Mg²⁺ content. Sm(Cr_0.77Mg_0.23)O₃ materials exhibit an excellent direct current electrical conductivity of 2.2×10³ S m⁻¹ at 1000°C.     

Synthesis and structure analysis of aluminum doped zinc oxide powders

Hexagonal Al-doped zinc oxide (ZnO) powders with a nominal composition of Zn1-xAlxO (0≤x≤0.028) were synthesized by the co-precipitation method. The contents of the Al element in the samples were measured by the inductively coupled plasma-optical emission spectroscopy (ICP-OES) technique. The structures of the Zn1-xAlxO (0≤x≤0.028) compounds calcined at 1000 and 1200℃ have been deter- mined using the Rietveld full-profile analysis method. Rietveld refinements of the diffraction data indi- cated that the addition of Al initially has a considerably positive effect on the decreasing of the lattice parameters a and c of Zn1-xAlxO, but the effect becomes very slight and even negative with the further increase of the Al content. The solid solubility limit of Al in ZnO (mole fraction y) is 2.2l%, resulting in Zn0.978Al0.22O. It seems that when the Al content is excessive, Al prefers to form a ZnAl2O4 compound with ZnO, but not to incorporate into the ZnO lattice to occupy the Zn2 cites. Two phases, [ZnO] (or Al-doped ZnO) and [ZnAl2O4], are obviously segregated in Zn1-xAlxO while the value of x is larger than 0.024. The UV-Vis absorption spectra show that the Al-doped ZnO exhibits a red-shift in the absorption edge without reduced transmission compared with pure ZnO, which also confirms that Al ions enter the ZnO lattice and form a Zn1-xAlxO solid solution.     

Influences of Co doping on the structural,optical and magnetic properties of ZnO nanorods synthesized by hydrothermal route

Pure and Co-doped ZnO nanorods have been synthesized by a hydrothermal process. The structure, morphology and properties of as-prepared samples have been studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectrometer as well as by superconducting quantum interference device (SQUID). The structure and morphology analyses show that Co doping can slightly impede the ZnO crystallinity, influence the nanorods morphology, but cannot change the preferred growth orientation of ZnO nanorods. The amount of Co doping contents is about 3.0 at% in ZnO nanorods and dopant Co²⁺ ions substitute Zn²⁺ ions sites in ZnO nanocrystal without forming any secondary phase. The optical measurements show that the Co doping can effectively tune energy band structure and enrich surface states in both UV and VL regions, which lead to novel PL properties of ZnO nanorods. In addition, ferromagnetic ordering of the as-synthesized Zn_1?xCo_xO nanorod arrays has been observed at room temperature, which should be ascribed to sp–d and d–d carrier exchange interactions and presence of abundant defects and oxygen vacancies.     

Crystal structures and magnetic properties of two-dimensional antiferromagnets Co1−xZnxTeMoO6

Crystal structures and magnetic properties of metal telluromolybdates Co_1−xZn_xTeMoO₆ (x=0.0, 0.1,…,0.9) are reported. All the compounds have an orthorhombic structure with space group P2₁2₁2 and a charge configuration of M²⁺Te⁴⁺Mo⁶⁺O₆. In this structure, M ions form a pseudo-two-dimensional lattice in the ab plane. Their magnetic susceptibility measurements have been performed in the temperature range between 1.8 and 300 K. The end member CoTeMoO₆ shows a magnetic transition at 24.4 K. The transition temperature for solid solutions rapidly decreases with increasing x and this transition disappears between x=0.4 and 0.5, which is corresponding to the percolation limit for the square-planer lattice. From the magnetization, specific heat, and powder neutron diffraction measurements, it is found that the magnetic transition observed in the CoTeMoO₆ is a canted antiferromagnetic ordering of Co²⁺ ions. The antiferromagnetic component of the ordered magnetic moment (3.12(3)μ_B at 10 K) is along the b-axis. In addition, there exists a small ferromagnetic component (0.28(3)μ_B) along the a-axis.     

Synthesis and electrical conductivity of perovskite-type PrCo1−xMgxO3

Oxides in the system PrCo_1−xMg_xO₃ (x=0.0, 0.05, 0.10, 0.15, 0.20, 0.25) were synthesized by citrate technique and characterized by powder X-ray diffraction and scanning electron microscope. All compounds have a cubic perovskite structure (space group ). The maximum ratio of doped Mg in the system PrCo_1−xMg_xO₃ is x=0.2. Further doping leads to the segregation of Pr₆O₁₁ in PrCo_1−xMg_xO₃. The substitution of Mg for Co improves the performance of PrCoO₃ as compared to the electrical conductivity measured by a four-probe electrical conductivity analyzer in the temperature range from 298 to 1073 K. The substitution of Mg for Co on the B site may be compensated by the formations of Co⁴⁺ and oxygen vacancies. The electrical conductivity of PrCo_1−xMg_xO₃ oxides increases with increasing x in the range of 0.0-0.2. The increase in conductivity becomes considerable at the temperatures ?673 K especially for x?0.1; it reaches a maximum at x=0.2 and 1073 K. From x>0.2 the conductivity of PrCo_1−xMg_xO₃ starts getting lower. This is probably a result of the segregation of Pr₆O₁₁ in PrCo_1−xMg_xO₃ , which blocks oxygen transport, and association of oxygen vacancies. A change in activation energy for all PrCo_1−xMg_xO₃ compounds (x=0-0.25) was observed, with a higher activation energy above 573 K and a lower activation energy below 573 K. The reasons for such a change are probably due to the change of dominant charge carriers from Co⁴⁺ to Vö in PrCo_1−xMg_xO₃ oxides and a phase transition mainly starting at 573 K.     

Structural and magnetic properties of Zn1−xSbxCr2−x/3Se4 (x=0.11, 0.16 and 0.20) single crystals

Single crystals of Zn_1−xSb_xCr_2−x/3Se₄ based on the ZnCr₂Se₄ spinel, which is known to exhibit interesting magnetic and electronic transport properties, have been prepared by solid state reaction from the appropriate selenides. Three compounds of different Sb content (x=0.11, 0.16, and 0.20) were studied by X-ray diffraction, X-ray photoelectron scattering technique and macroscopic magnetic measurements with the aim to determine (i) stability of the cubic symmetry and (ii) influence of the Sb admixture on the magnetic properties. The results show that the Sb³⁺ and Zn²⁺ ions share the tetrahedral sites in the spinel structure, while the Cr³⁺ions carrying magnetic moments, are located in the octahedral sites. The X-ray photoelectron spectroscopy (XPS) data indicate that in this series of compounds the chromium ions have a 3d³ electronic configuration. The three samples studied order antiferromagnetically at low temperatures, with the magnetic characteristics being hardly altered with respect to those reported for the parent ZnCr₂Se₄ compound.