The crystallization kinetics of Co doping on Ni–Mn–Sn magnetic shape memory alloy thin films

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films. However, the Co doping effect on the crystallization process of the Ni–Mn–Sn alloy thin films is important but not clear. Therefore, we investigate the influence of Co doping on the crystallization kinetics for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) magnetic shape memory alloy thin films by DSC analysis. For the non-isothermal process, each DSC curve has a single exothermic peak, which is asymmetrical. The crystallization peak temperatures and the activation energy of thin films both rise gradually with increasing Co content. Then, the activation energy of Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films obtained by the Kissinger equation method is determined as 157.9 kJ mol⁻¹, 198.8 kJ mol⁻¹, 213 kJ mol⁻¹ and 253.6 kJ mol⁻¹, respectively. The local activation energy of thin films with different Co content show the different variation tendency. In the isothermal crystallization, the average of the Avrami exponent n for thin films of each Co content is approximately 1.5, suggesting that the mechanism of crystallization is two-dimensional diffusion-controlled growth for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films.

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films.     

Cu(i) substituted wurtzite ZnO: a novel room temperature lead free ferroelectric and high-κ giant dielectric

Semiconducting wurtzite ZnO, with the highest incipient piezoelectricity is an attractive alternative choice with doping transition metal ions in the host lattice to develop novel binary ferroelectric materials that can be easily fabricated in any device architecture. Up to 8% Cu⁺ ion substitution on Zn²⁺ sites in the ZnO lattice was achieved by careful selection of raw material and adaptation of a low temperature sol–gel synthesis route for the preparation of bulk material. Phase purity and substitution of Cu⁺ ions in the ZnO lattice along with oxide-ion vacancy formation was confirmed using Powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray analysis (EDX), X-ray Photoelectron Spectroscopy (XPS) and Magnetic property measurement system (MPMS) studies. A giant dielectric constant (∼6300) was observed at 600 °C for Zn_0.95Cu_0.05O_1−δ pellets at 100 kHz frequency. Bulk Zn_0.95Cu_0.05O_1−δ also exhibits ferroelectricity at room temperature with remnant polarization P_r and V_c equal to 9.60 × 10⁻³ μC cm⁻² and 3.83 × 10² V cm⁻¹ respectively.

Cu⁺ ion substituted ZnO, Zn_1−xCu_xO_1−δ have shown high dielectric constant (∼6300) at 600 °C at 100 kHz frequency and ferroelectricity at room temperature than for bulk Zn_0.95Cu_0.05O_1−δ samples.     

A simple synthesis of transparent and highly conducting p-type CuxAl1−xSy nanocomposite thin films as the hole transporting layer for organic solar cells

Inorganic p-type films with high mobility are very important for opto-electronic applications. It is very difficult to synthesize p-type films with a wider, tunable band gap energy and suitable band energy levels. In this research, p-type copper aluminum sulfide (Cu_xAl_1−xS_y) films with tunable optical band gap, carrier density, hole mobility and conductivity were first synthesized using a simple, low cost and low temperature chemical bath deposition method. These in situ fabricated Cu_xAl_1−xS_y films were deposited at 60 °C using an aqueous solution of copper(ii) chloride dihydrate (CuCl₂·2H₂O), aluminium nitrate nonohydrate [Al(NO₃)₃·9H₂O], thiourea [(NH₂)₂CS], and ammonium hydroxide, with citric acid as the complexing agent. Upon varying the ratio of the precursor, the band gap of the Cu_xAl_1−xS_y films can be tuned from 2.63 eV to 4.01 eV. The highest hole mobility obtained was 1.52 cm² V⁻¹ s⁻¹ and the best conductivity obtained was 546 S cm⁻¹. The Cu_xAl_1−xS_y films were used as a hole transporting layer (HTL) in organic solar cells (OSCs), and a good performance of the OSCs was demonstrated using the Cu_xAl_1−xS_y films as the HTL. These results demonstrate the remarkable potential of Cu_xAl_1−xS_y as hole transport material for opto-electronic devices.

Inorganic p-type films with high mobility are very important for opto-electronic applications.     

Composite formation in CdSe:Cu2Se nanocrystal films,charge transport characteristics and heterojunction performance

The use of nanocrystals as materials for potential technological applications depends on tailoring their properties through intentional doping with external impurities. We have used a new technique to synthesize nanocrystal thin films of CdSe:Cu₂Se containing different weight percentages (wt%) of Cu₂Se. The films were deposited on glass substrates at room temperature by co-evaporation of CdSe and Cu₂Se powder in nitrogen gas at a pressure larger than that required for conventional thin film deposition. The films consisted of nanograins of CdSe doped with Cu₂Se (i.e., nanograins of Cd_1−xCu_2(x)Se where x is the atom% of Cu₂Se doped into CdSe) for lower wt% of Cu₂Se, and nanocomposites of Cd_1−xCu_2(x)Se and Cu₂Se for higher wt% of Cu₂Se. An energy band diagram built using the Anderson model was used for discussing the heterojunction characteristics of the junction between nanograins of Cd_1−xCu_2(x)Se and Cu₂Se. To investigate the usefulness of the nanocrystal thin films of CdSe:Cu₂Se for practical applications, the I–V characteristics of p–p and p–n hetero-junctions formed by the films respectively with nanostructured films of similarly deposited Cu₂Se and CdSe films were studied.

The use of nanocrystals as materials for potential technological applications depends on tailoring their properties through intentional doping with external impurities.     

The effects of microstructure,Nb content and secondary Ruddlesden–Popper phase on thermoelectric properties in perovskite CaMn1−xNbxO3 (x = 0–0.10) thin films

CaMn_1−xNb_xO₃ (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn_1−x,Nb_x)O thin films were deposited on 1$\bar{1}$00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn_1−xNb_xO₃ films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn_1−xNb_x)O to orthorhombic during post-deposition annealing at 700 °C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO₃ showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden–Popper (R–P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn_1−xNb_xO₃. The electrical resistivity and Seebeck coefficient of the pure CaMnO₃ film were measured to 2.7 Ω cm and −270 μV K⁻¹ at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 Ω cm and −145 μV K⁻¹ for x = 0.05. Yielding a power factor of 21.5 μW K⁻² m⁻¹ near room temperature, nearly eight times higher than for pure CaMnO₃ (2.8 μW K⁻² m⁻¹). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R–P phase. The thermal conductivity of the CaMn_1−xNb_xO₃ films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m⁻¹ K⁻¹. The low thermal conductivity is attributed to grain boundary scattering and the secondary R–P phase.

Reduction of thermal conductivity of sputtered CaMn_1−xNb_xO₃ thin films by secondary Ruddlesden–Popper phase and grain size optimization.     

Tuning the microstructural and magnetic properties of CoFe2O4/SiO2 nanocomposites by Cu2+ doping

Co–Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.3) nanoparticles (NPs) embedded in a SiO₂ matrix were prepared by a sol–gel method. The effect of a small Cu²⁺ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mössbauer spectroscopy, and VSM. It was found that single cubic Co_1−xCu_xFe₂O₄ ferrite was formed in amorphous SiO₂ matrix. The average crystallite size of Co_1−xCu_xFe₂O₄ increased from 18 to 36 nm as Cu²⁺ doping content x increased from 0 to 0.3. Mössbauer spectroscopy indicated that the occupancy of Cu²⁺ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu²⁺doping resulted in cation migration between octahedral A and tetrahedral B sites. With Cu²⁺ content increasing, the saturation magnetization (M_s) first increased, then tended to decrease, while the coercivity (H_c) decreased continuously, which was associated with the cation migration. The results suggest that the Cu²⁺ doping content in Co_1−xCu_xFe₂O₄ NPs plays an important role in its magnetic properties.

The Cu²⁺ doping content in Co_1−xCu_xFe₂O₄/SiO₂ plays an important role in tuning hyperfine interaction and magnetic properties.     

Roll-to-roll sputtered and patterned Cu2−xO/Cu/Cu2−xO multilayer grid electrode for flexible smart windows

We fabricated cost-effective Cu_2−xO/Cu/Cu_2−xO multilayer grid electrodes using roll-to-roll (RTR) sputtering and patterning processes for use as transparent and flexible electrodes in flexible smart windows. To optimize the patterned Cu_2−xO/Cu/Cu_2−xO multilayer grid, the electrical and optical properties of the Cu_2−xO/Cu/Cu_2−xO multilayer grid electrodes were investigated as a function of grid width and pitch, which directly influence the filling factor of the grid. At the optimized grid width of 16 and pitch of 600 μm, the Cu_2−xO/Cu/Cu_2−xO multilayer grid had a sheet resistance of 7.17 Ohm per square and an optical transmittance of 87.6%. In addition, the mechanical properties of the optimized Cu_2−xO/Cu/Cu_2−xO multilayer grid electrode was compared to those of brittle ITO electrodes to demonstrate its outstanding flexibility. To show the potential of the Cu_2−xO/Cu/Cu_2−xO multilayer grid for smart windows, we fabricated a flexible and transparent thin film heater (TFH) and a flexible electrochromic (EC) device, which are key components of smart windows. The low saturation voltage of the Cu_2−xO/Cu/Cu_2−xO grid-based TFH and the fast on–off performance of the Cu_2−xO/Cu/Cu_2−xO grid-based EC device indicates that the RTR-processed Cu_2−xO/Cu/Cu_2−xO multilayer grid is promising as a low-cost and large-area flexible transparent electrode for high-performance smart windows.

We fabricated cost-effective Cu_2−xO/Cu/Cu_2−xO multilayer grid electrodes using roll-to-roll (RTR) sputtering and patterning processes for use as transparent and flexible electrodes in flexible smart windows.     

Mixed metal CoII1−xZnIIx–organic frameworks based on chains with mixed carboxylate and azide bridges: magnetic coupling and slow relaxation

A series of isomorphous three-dimensional metal–organic frameworks [Co^II_1−xZn^II_x(L)(N₃)]·H₂O (x = 0.26, 0.56 and 0.85) based on bimetallic Co^II_1−xZn^II_x (x = 0.26, 0.56 and 0.85) chains with random metal sites have been synthesized and magnetically characterized. The Co^II_1−xZn^II_x series, which intrinsically feature random anisotropic/diamagnetic sites, shows complex magnetic interactions. By gradually introducing the diamagnetic Zn^II ions into the pure anisotropic Co^II single-chain magnets system, the ferromagnetic interactions between Co^II ions are gradually diluted. Moreover, the slow magnetic relaxation behaviour of the mixed metal Co^II_1−xZn^II_x systems also changes. In this bimetallic series Co^II_1−xZn^II_x, the Co-rich materials exhibit slow relaxation processes that may arise from SCM mechanism, while the Zn^II-rich materials show significantly low slow magnetic relaxation. A general trend is that the activation energy and the blocking temperature decrease with the increase in diamagnetic Zn^II content, emphasizing the importance of anisotropy for slow relaxation of magnetization.

A series of mixed-metal systems consisting of Co^II_1−xZn^II_x chains with (μ-COO)₂(μ-EO-N₃) bridges were prepared, exhibiting interesting magnetic coupling and slow magnetic relaxation.     

Chemical solution deposition of Y1−xGdxBa2Cu3O7−δ–BaHfO3 nanocomposite films: combined influence of nanoparticles and rare-earth mixing on growth conditions and transport properties

Y_1−xGd_xBa₂Cu₃O_7−δ–BaHfO₃ (YGBCO–BHO) nanocomposite films containing 12 mol% BHO nanoparticles and different amounts of Gd were prepared by chemical solution deposition following the trifluoroacetic route on SrTiO₃ single crystals in order to study the influence of the rare earth stoichiometry on structure, morphology and superconducting properties of these films. We optimized the growth process for each of several Gd contents of the 220 nm thick YGBCO–BHO films by varying crystallization temperature and oxygen partial pressure. This optimization process led to the conclusion that mixing the rare earths in YGBCO–BHO films leads to wider growth parameter windows compared to YBCO-BHO and GdBCO-BHO films giving larger freedom for selecting the most convenient processing parameters in order to adapt to different substrates or applications which is very important for the industrial production of coated conductors. The optimized films show a continuous increase of T_c with Gd content x from ∼90 K for the YBCO-BHO films to ∼94 K for the GdBCO-BHO films. Consequently, an increase of the 77 K self-field J_c with Gd content is observed reaching values > 7 MA cm⁻² for Gd contents x > 0.5. The transport properties of these films under applied magnetic fields are significantly improved with respect to the pristine YBCO films. All YGBCO–BHO nanocomposite films grew epitaxially with c-axis orientation and excellent out-of-plane and in-plane texture. The films are dense with a low amount of pores and only superficial indentations.

Superconducting Y_1–xGd_xBa₂Cu₃O_7–δ–BaHfO₃ nanocomposite films were prepared by chemical solution deposition on SrTiO₃ substrates in order to study the influence of the rare earth stoichiometry on their structure, morphology and electrical properties.     

Composite photocatalysts based on Cd1−xZnxS and TiO2 for hydrogen production under visible light: effect of platinum co-catalyst location

Ternary composite photocatalysts based on titania and solid solutions of CdS and ZnS were prepared and studied by a set of physicochemical methods including XRD, XPS, HRTEM, UV-vis spectroscopy, and electrochemical tests. Two synthetic techniques of platinization of Cd_1−xZn_xS/TiO₂ were compared. In the first case, platinum was deposited on the surface of synthesized Cd_1−xZn_xS (x = 0.2–0.3)/TiO₂ P25; in the second one, Cd_1−xZn_xS (x = 0.2–0.3) was deposited on the surface of Pt/TiO₂ P25. The photocatalytic properties of the obtained samples were compared in the hydrogen evolution from TEOA aqueous solution under visible light (λ = 425 nm). The Cd_1−xZn_xS (10–50 wt%; x = 0.2–0.3)/Pt (1 wt%)/TiO₂ photocatalysts demonstrated much higher photocatalytic activity than the Pt (1 wt%)/Cd_1−xZn_xS (10–50 wt%; x = 0.2–0.3)/TiO₂ ones. It turned out that the arrangement of platinum nanoparticles precisely on the titanium dioxide surface in a composite photocatalyst makes it possible to achieve efficient charge separation according to the type II heterojunctions and, accordingly, a high rate of hydrogen formation. The highest photocatalytic activity was demonstrated by 20% Cd_0.8Zn_0.2S/1% Pt/TiO₂ in the amount of 26 mmol g⁻¹ h⁻¹ (apparent quantum efficiency was 7.7%) that exceeds recently published values for this class of photocatalysts.

The determination of the preferred location of platinum particles in TiO₂–Cd_1−xZn_xS systems was carried out for the first time.     

Enhanced thermoelectric properties of hydrothermally synthesized Bi0.88−xZnxSb0.12 nanoalloys below the semiconductor–semimetal transition temperature

Bi_0.88−xZn_xSb_0.12 alloys with x = 0.00, 0.05, 0.10, and 0.15 were prepared using hydrothermal synthesis in combination with evacuating-and-encapsulating sintering. The effects of partial Zn substitution for Bi and different sintering temperatures on the thermoelectric properties of Bi_0.88−xZn_xSb_0.12 alloys were investigated between 25 K and 425 K. Both the electrical conductivity and absolute thermopower are enhanced for the set of alloys sintered at 250 °C. The maximum power factor of 57.60 μW cm⁻¹ K⁻² is attained for the x = 0.05 alloy sintered at 250 °C. As compared with Zn-free Bi_0.88Sb_0.12, both the total thermal conductivity and lattice component are reduced upon Zn doping. Bipolar conduction is observed in both electronic and thermal transport. The maximum zT of 0.47 is attained at 275 K for the x = 0.05 alloy sintered at 250 °C.

The peak zT is attained for hydrothermally synthesized Bi_0.83Zn_0.05Sb_0.12 nanoalloy due to the significantly enhanced thermoelectric power factor and relatively low thermal conductivity.     

Improved ferroelectric properties and band-gap tuning in BiFeO3 films via substitution of Mn

Multiferroic BiFe_1−xMn_xO₃ (x = 0, 0.04, 0.08, 0.12) films have been prepared on Pt/Ti/SiO₂/Si and ITO/glass substrates via the solution-gelation technique. The impacts of Mn doping of BFO thin films on the structure, morphology, leakage current, ferroelectric properties and optical band gap have been systematic investigated. From the XRD patterns, all samples match well with the perovskite structure without an impurity phase and the thin films exhibit dense and smooth microstructure. A leakage current density of 1.10 × 10⁻⁶ A cm⁻² which is about four orders of magnitude lower than that of pure BiFeO₃ was observed for the 8% Mn doped BFO thin film at an external electric field <150 kV cm⁻¹. An increase in the remnant polarization with Mn substitution was observed, with a maximum value of ∼19 μC cm⁻² for the 8% Mn-substituted film. Moreover, optical absorption spectra indicate that the doping of Mn has an effect on the energy band structure. Compared with pure BiFeO₃, Mn doped thin films present an intense red shift as shown in the UV-visible diffuse absorption together with the decreased direct and indirect optical band gaps. In addition, this work gives insight into the relationship between ferroelectric remnant polarization and band-gap and finds that the optical band gap decreases with the increase of residual polarization.

Multiferroic BiFe_1−xMn_xO₃ (x = 0, 0.04, 0.08, 0.12) films have been prepared on Pt/Ti/SiO₂/Si and ITO/glass substrates via the solution-gelation technique.     

Colloidal CdxZn1−xS nanocrystals as efficient photocatalysts for H2 production under visible-light irradiation

Cd_xZn_1−xS nanocrystals with sizes ranging from 3–11 nm were synthesized by a simple organic solution method. The nanocrystals possess a cubic zinc-blende structure and the bandgap blue-shifts from 2.1 eV to 3.4 eV by increasing the composition of Zn ions in the solid solutions. After a facile ligand exchange process, the photocatalytic activity for H₂ production of the Cd_xZn_1−xS nanocrystals was investigated under visible-light irradiation (λ ≥ 420 nm) with Na₂SO₃/Na₂S as the electron donor. It was found that the Cd_0.8Zn_0.2S had the highest photoactivity with H₂ evolution rate of 6.32 mmol g⁻¹ h⁻¹. By in situ adding Pt precursors into the reaction solution, inhomogenous Pt–Cd_xZn_1−xS nanoheterostructures were formed, which accounted for a 30% enhancement for the H₂ evolution rate comparing with that of pure Cd_0.8Zn_0.2S nanocrystals. This work highlights the use of facile organic synthesis in combination with suitable surface modification to enhance the activity of the photocatalysts.

Colloidal Cd_xZn_1−xS and Pt–Cd_xZn_1−xS nanocrystals by simple organic solution method show efficient photocatalytic H₂-evolution performance.     

Thermoelectric performance enhancement of eco-friendly Cu2Se through incorporating CB4

We have prepared Cu₂Se + x wt% CB₄ composites with x = 0, 0.1, 0.3, 0.5, and 0.7 by a hydrothermal method and hot-pressing technique. The structural and compositional analysis indicates that pure phase Cu₂Se powders were synthesized and the densified layered bulk samples were obtained. Electrical properties testing showed that the sample with x = 0.5 has the high power factor of 0.886 mW m⁻¹ K⁻² due to its high Seebeck coefficient. Meanwhile, the thermal conductivity was suppressed to 0.6 W m⁻¹ K⁻¹ at 773 K. As a result, the final optimized ZT value of 1.46 at 773 K was achieved. These results suggest that CB₄ could be an alternative inclusion to improve effectively the thermoelectric performance of Cu₂Se.

Thermoelectric performance enhancement in a liquid-like material Cu₂Se by introducing CB₄ nanopowders based on the hydrothermal method and hot-pressing technique.     

Designing coexisting multi-phases in PZT multilayer thin films: an effective way to induce large electrocaloric effect

Coexisting multi-phases in PbZr_xTi_1−xO₃ multilayer thin films were successfully fabricated using the sol–gel method. The microstructure and electrical of the multilayer films with different growth sequences, including the up multilayer films and down multilayer films, have been systematically investigated. The results indicate that a large electrocaloric effect (ECE) is obtained at the temperatures much below the Curie temperature. At room temperature (25 °C), the change in temperature (ΔT) values of the up multilayer and down multilayer thin films are 20.2 K with the applied electric field E = 826 kV cm⁻¹ and 46.3 K with the E = 992 kV cm⁻¹, respectively. In addition, both the films exhibit outstanding ECE of around 145 °C, and ΔT values of 28.9 K and 14.8 K have been obtained for the up multilayer and down multilayer thin films. The results indicate that the antiferroelectric/ferroelectric (AFE/FE), ferroelectric/ferroelectric (FE/FE) phase transition and the synergistic effect of the AFE/FE and FE/FE phase transition are as effective as the FE/PE phase transition. In particular, the multilayer thin films are endowed with refrigeration ability at multi-temperature zones due to the coexistence of multi-phases.

Coexisting multi-phases in PbZr_xTi_1−xO₃ multilayer thin films were successfully fabricated using the sol–gel method.     

Facile preparation of ZnxCd1−xS/ZnS heterostructures with enhanced photocatalytic hydrogen evolution under visible light

Hydrogen evolution from water using solar energy is regarded as a most promising process, thus, exploring efficient photocatalysts for water splitting is highly desirable. To avoid the rapid recombination of photogenerated electrons and holes in CdZnS semiconductors, Zn_xCd_1−xS/ZnS composites were synthesized via a one-step hydrothermal method and then annealed at 400 °C for 60 min under argon flow. Zn_xCd_1−xS/ZnS composites are composed of ZnS nanosheets decorated with Zn_xCd_1−xS nanorods, and TEM and UV-vis absorption spectra confirm the formation of the heterostructure between Zn_xCd_1−xS nanorods and ZnS nanosheets. Because of the well-matched band alignment, stronger optical absorption and larger carrier density, Zn_0.2Cd_0.8S/ZnS has the highest hydrogen production, with a photocatalytic hydrogen production rate up to 16.7 mmol g⁻¹ h⁻¹ under visible light irradiation. Moreover, the photocatalyst also exhibits high stability and good reusability for hydrogen production reaction. The facile and efficient approach for ZnS based heterostructures could be extended to other metal compound materials.

Schematic illustration for electron charge transfer and H₂ evolution mechanism for the Zn_0.2Cd_0.8S/ZnS nanocomposites.     

Copper-doped lanthanum manganite La0.65Ce0.05Sr0.3Mn1−xCuxO3 influence on structural,magnetic and magnetocaloric effects

Bulk nanocrystalline samples of La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method. The effect of the substitution for Mn with Cu upon the structural and magnetic properties has been investigated by means of X-ray diffraction (XRD), Raman spectroscopy and dc magnetization measurements. The structural parameters obtained using Rietveld refinement of XRD data showed perovskite structures with rhombohedral (R$\bar{3}$c) symmetry without any detectable impurity phase. Raman spectra at room temperature reveal a gradual change in phonon modes with increasing copper concentration. The analysis of the crystallographic data suggested a strong correlation between structure and magnetism, for instance a relationship between a distortion of the MnO₆ octahedron and the reduction in the Curie temperature, T_c. A paramagnetic to ferromagnetic phase transition at T_C is observed. The experimental results confirm that Mn-site substitution with Cu destroys the Mn³⁺–O²⁻–Mn⁴⁺ bridges and weakens the double exchange (DE) interaction between Mn³⁺ and Mn⁴⁺ ions, which shows an obvious suppression of the FM interaction in the La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ matrix. The maximum magnetic entropy change −ΔS^max_M is found to decrease with increasing Cu content from 4.43 J kg⁻¹ K⁻¹ for x = 0 to 3.03 J kg⁻¹ K⁻¹ for x = 0.15 upon a 5 T applied field change.

Bulk nanocrystalline samples of La_0.65Ce_0.05Sr_0.3Mn_1−xCu_xO₃ (0 ≤ x ≤ 0.15) manganites are prepared by the sol–gel based Pechini method.     

Syntheses,crystal structures,magnetic properties and ESI-MS studies of a series of trinuclear CuIIMIICuII compounds (M = Cu,Ni, Co,Fe, Mn,Zn)

Six trinuclear Cu^IIM^IICu^II compounds (M = Cu, Ni, Co, Fe, Mn, Zn) derived from the Schiff base ligand, H₂L (2 + 1 condensation product of salicylaldehyde and trans-1,2-diaminocyclohexane) are reported in this investigation. The composition of the metal complexes are [{Cu^IIL(ClO₄)}₂Cu^II(H₂O)]·2H₂O (1), [{Cu^IIL(ClO₄)}{Ni^II(H₂O)₂}{Cu^IIL}]ClO₄·CH₃COCH₃ (2), [{Cu^IIL(ClO₄)}{Co^II(CH₃COCH₃)(H₂O)}{Cu^IIL(CH₃COCH₃)}]ClO₄ (3) and isomorphic [{Cu^IIL(ClO₄)}₂M^II(CH₃OH)₂] (4, M = Fe; 5, M = Mn; 6, M = Zn). Two copper(ii) ions in 1–6 occupy N₂O₂ compartments of two L²⁻ ligands, while the second metal ion occupies the O(phenoxo)₄ site provided by the two ligands, i.e., the two metal ions in both Cu^IIM^II pairs are diphenoxo-bridged. Positive ESI-MS of 1–6 reveals some interesting features. Variable-temperature and variable-field magnetic studies reveal moderate or weak antiferromagnetic interactions in 1–6 with the following values of magnetic exchange integrals (H = −2JS₁S₂ type): J₁ = −136.50 cm⁻¹ and J = 0.00 for the Cu^IICu^IICu^II compound 1; J₁ = −22.16 cm⁻¹ and J = −1.97 cm⁻¹ for the Cu^IINi^IICu^II compound 2; J₁ = −14.78 cm⁻¹ and J = −1.86 cm⁻¹ for the Cu^IICo^IICu^II compound 3; J₁ = −6.35 cm⁻¹ and J = −1.17 cm⁻¹ for the Cu^IIFe^IICu^II compound 4; J₁ = −6.02 cm⁻¹ and J = −1.70 cm⁻¹ for the Cu^IIMn^IICu^II compound 5; J = −2.25 cm⁻¹ for the Cu^IIZn^IICu^II compound 6 (J is between two Cu^II in the N₂O₂ compartments; J₁ is between Cu^II and M^II through a diphenoxo bridge).

Six homo/heterotrinuclear Cu^IIM^IICu^II (M = Mn–Zn) compounds derived from salicylaldehyde-trans-1,2-diaminocyclohexane, which is a rarely utilized ligand, are reported.     

Structural,optical and dielectric properties of tellurium-based double perovskite Sr2Ni1−xZnxTeO6

In this paper, Sr₂Ni_1−xZn_xTeO₆ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) double perovskite compounds were synthesised by the conventional solid-state method, and the structural, optical and dielectric properties were investigated. The Rietveld refinement of X-ray diffraction data shows that all compounds were crystallised in monoclinic symmetry with the I2/m space group. Morphological scanning electron microscopy reported that the grain sizes decreased as the dopant increased. The UV-vis diffuse reflectance spectroscopy conducted for all samples found that the optical band gap energy, E_g, increased from 3.71 eV to 4.14 eV. The dielectric permittivity ε′ values increased for the highest Zn-doped composition, Sr₂Ni_0.2Zn_0.8TeO₆, being ∼1000 and ∼60 in the low- and high-frequency range, respectively. All samples exhibited low dielectric loss (tan δ ≤ 0.20) in the range of 10⁴–10⁵ Hz frequency. Impedance measurement revealed that grain resistance decreased with enhancement in Zn content in the Sr₂NiTeO₆ crystal lattice.

In this paper, Sr₂Ni_1−xZn_xTeO₆ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) double perovskite compounds were synthesised by the conventional solid-state method, and the structural, optical and dielectric properties were investigated.     

Synthesis and characterisation of Ba(Zn1−xCox)2Si2O7 (0 ≤ x ≤ 0.50) for blue-violet inorganic pigments

Ba(Zn_1−xCo_x)₂Si₂O₇ (0 ≤ x ≤ 0.50) solid solutions were synthesized as novel blue-violet inorganic pigments by a conventional solid-state reaction method. The crystal structure, optical properties, and colour of the pigments were characterized. All the pigments were obtained in a single-phase form. The pigments strongly absorbed visible light at wavelengths from 550 to 650 nm, corresponding to the range of green to orange light. This optical absorption was caused by the d–d transition of the tetrahedrally coordinated Co²⁺ (⁴A₂(F) → ⁴T₁(P)), which was the origin of the blue-violet colour of the pigments. The most intense colour was obtained for Ba(Zn_0.85Co_0.15)₂Si₂O₇, where a* = +52.2 and b* = −65.5 in the CIE (Commission Internationale de l''Éclairage) L*a*b* system. These absolute values were significantly larger than those of commercial violet pigments such as Co₃(PO₄)₂ (a* = +33 and b* = −32) and NH₄MnP₂O₇ (a* = +39 and b* = −21). Therefore, the Ba(Zn_0.85Co_0.15)₂Si₂O₇ pigment could be a novel blue-violet inorganic pigment.

Ba(Zn_1−xCo_x)₂Si₂O₇ (0 ≤ x ≤ 0.50) solid solutions were synthesized as blue-violet inorganic pigments and the colour gradually changed from pale blue-violet to deep blue-violet with increasing the Co²⁺ concentration.