Single‐Junction Polymer Solar Cells with 16.35% Efficiency Enabled by a Platinum(II) Complexation Strategy

A new strategy of platinum(II) complexation is developed to regulate the crystallinity and molecular packing of polynitrogen heterocyclic polymers, optimize the morphology of the active blends, and improve the efficiency of the resulting nonfullerene polymer solar cells (NF‐PSCs). The newly designed s‐tetrazine (s‐TZ)‐containing copolymer of PSFTZ (4,8‐bis(5‐((2‐butyloctyl)thio)‐4‐fluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐3,6‐bis(4‐octylthiophen‐2‐yl)‐1,2,4,5‐tetrazine) has a strong aggregation property, which results in serious phase separation and large domains when blending with Y6 ((2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile)), and produces a power‐conversion efficiency (PCE) of 13.03%. By adding small amount of Pt(Ph)₂(DMSO)₂ (Ph, phenyl and DMSO, dimethyl sulfoxide), platinum(II) complexation would occur between Pt(Ph)₂(DMSO)₂ and PSFTZ. The bulky benzene ring on the platinum(II) complex increases the steric hindrance along the polymer main chain, inhibits the polymer aggregation strength, regulates the phase separation, optimizes the morphology, and thus improves the efficiency to 16.35% in the resulting devices. 16.35% is the highest efficiency for single‐junction PSCs reported so far.     

Synthesis and magnetic properties of one-dimensional metal oxalate networks as molecular-based magnets

The homo- and heteropolymetallic assemblies of MM′(OX)₂(H₂O)₄, where MM′ represents MnMn, CoMn, NiMn, CuMn, CoCo, NiCo, CuCo, NiNi, CuNi, and CuCu; and the respective complexes, numbered 1–10, have been prepared by reacting metal(II) salts-i.e. of Mn, Co, Ni, and Cu^- and potassium oxalate monohydrate in hot water (90–100°C). The magnetic susceptibility data of the complexes 8 and 9 in the 300 K-20 K temperature range obeys the Curie-Weiss law and exhibits Weiss constants -50 K and -100 K, respectively. On lowering the temperature, the effective magnetic moment decreases gradually and is indicative of antiferromagnetic phase transition. The complexes have also been characterized by ES mass spectrometry, infrared (IR), electronic, and electron spin resonance (ESR) spectra. Most of the work was presented at the ‘5th IUMRS International Conference in Asia’ held at IISc, Bangalore during October 13–16, 1998     

Synthesis,characterization, and photovoltaic properties of acceptor–donor–acceptor organic small molecules with different terminal electron-withdrawing groups

Two soluble acceptor–donor–acceptor (A–D–A) type organic small molecules, 2,2′-(5,5′-(1E,1′E)-2,2′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(ethene-2,1-diyl)bis(3,4-dihexylthiophene-5,2-diyl))bis(methan-1-yl-1-ylidene)dimalononitrile (BvT-DCN) and 2,2′-(3,3′-(1E,1′E)-2,2′-(5,5′-(1E,1′E)-2,2′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(ethene-2,1-diyl)bis(3,4-dihexylthiophene-5,2-diyl))bis(ethene-2,1-diyl)bis(5,5-dimethylcyclohex-2-ene-3-yl-1-ylidene))dimalononitrile (BT-C6), were synthesized by Knoevenagel condensation reaction based on benzothiadiazole, thiophene, and different terminal electron-withdrawing groups. The acceptor group benzothiadiazole and donor group thiophene inside the molecules are connected by all-trans double bonds, which ensures the benzothiadiazole and thiopene groups are in the same plane and makes the molecules have a relative narrow band gap and absorb sunlight in the long wavelength. The terminal electron-withdrawing groups, malononitrile and 2-(5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCM), are symmetrically introduced into the molecules, respectively, to tune the energy level and extend the absorption of the molecules. The UV–Vis absorption spectrum and cyclic voltammetry measurements indicated that BT-C6 has a lower energy band gap (1.60 eV) than BvT-DCN (1.71 eV), which arises from the stronger electron-withdrawing ability of DCM group in BT-C6 than that of malononitrile group in BvT-DCN. And BvT-DCN and BT-C6 have nearly the same highest occupied molecular orbital energy level, ?5.74 eV for BvT-DCN and ?5.72 eV for BT-C6 due to the same electron–donor group of the two compounds. Bulk heterojunction photovoltaic devices were fabricated using BvT-DCN or BT-C6 as donor and (6,6)-phenyl C₆₁-butyric acid methyl ester as acceptor. The device based on BT-C6 has a higher (~8 times) short circuit current and power conversion efficiency than the device based on BvT-DCN, resulting from the wider solar light absorption of BT-C6 and smaller phase separation dimension of the active layer based on BT-C6.     

Enhanced optoelectronics properties of europium(III) complexes with β-diketone and nitrogen heterocyclic ligands

Preparation and photoluminescence behavior of six new europium complexes with β-diketone 1-(2-hydroxy phenyl)-3-phenylpropane-1,3-dione (HPPP) and bathophenanthroline (batho), 2,2′-bipyridyl (bipy), 2,2′-biquinoline (biq), neocuproin (neo) and 1,10-phenanthroline (phen) are reported in solid state. The ligand (HPPP) and complexes Eu(HPPP)₃·H₂O (1), Eu(HPPP)₃·phen (2), Eu(HPPP)₃·batho (3), Eu(HPPP)₃·bipy (4), Eu(HPPP)₃·biq (5) and Eu(HPPP)₃·neo (6) were characterized by means of elemental analysis, infrared spectroscopy, proton nuclear magnetic resonance (¹H-NMR). The optical properties, thermal stability and crystalline nature were investigated by photoluminescence spectroscopy, thermogravimetric analysis and XRD respectively. The emission spectra show narrow intense emission band of central europium (III) metal ion that arise from the high intense ⁵D₀ → ⁷F₀ transition. The introduction of ancillary ligands like batho, bipy, biq, neo, phen enlarged the π-conjugation system in complexes as a result higher luminescence intensity, longer life time (τ) and higher quantum efficiency (η) observed in europium ternary complexes in comparison to Eu(HPPP)₃·H₂O (1). Based on the emission spectra, the luminescence decay curve was measured which indicated that the transfer of energy from HPPP ligand to the europium metal is more efficient in complexes 2–6 than complex 1.     

Two Well‐Miscible Acceptors Work as One for Efficient Fullerene‐Free Organic Solar Cells

High‐performance ternary organic solar cells are fabricated by using a wide‐bandgap polymer donor (bithienyl‐benzodithiophene‐alt‐fluorobenzotriazole copolymer, J52) and two well‐miscible nonfullerene acceptors, methyl‐modified nonfullerene acceptor (IT‐M) and 2,2′‐((2Z ,2′Z )‐((5,5′‐(4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydros‐indaceno[1,2‐b :5,6‐b ′]dithiophene‐2,7‐diyl)bis(4‐((2‐ethylhexyl)oxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H ‐indene‐2,1‐diylidene))dimalononitrile (IEICO). The two acceptors with complementary absorption spectra and similar lowest unoccupied molecular orbital levels show excellent compatibility in the blend due to their very similar chemical structures. Consequently, the obtained ternary organic solar cells (OSC) exhibits a high efficiency of 11.1%, with an enhanced short‐circuit current density of 19.7 mA cm^?2 and a fill factor of 0.668. In this ternary system, broadened absorption, similar output voltages, and compatible morphology are achieved simultaneously, demonstrating a promising strategy to further improve the performance of ternary OSCs.     

Insights into the selective sensing mechanism of a luminescent Cd(II)-based MOF chemosensor toward NACs: roles of the host–guest interactions and PET processes

Journal of Materials Science - The structural and photophysical properties of the [Cd2(H2L)2(H2O)5].5H2O (where H4L is the ligand 5,5'-((thiophene-2,5-dicarbonyl)bis(azanediyl))diisophthalic...     

Synthesis, spectroscopy and magnetic properties of transition-metal complexes with aminophosphonate derivatives of pyridine

The compounds of general formula [ML₂](ClO₄)₂ [M = Cu(II), Ni(II), Co(II)]; L = diethyl 3-pyridylmethyl[N-(butyl)amino]phosphonate (3-pmape) or diethyl 4-pyridylmethyl[N-(butyl)amino]phosphonate (4-pmape) were prepared. The new complexes were identified and characterized by elemental analysis, infrared, electronic spectral studies and magnetic measurements. The complexes are sixcoordinate. Metal ions are octahedrally surrounded by two pyridine and two amine nitrogens, and two oxygens of the phosphoryl groups. The results of the magnetic studies suggest polymeric chain structure of the above complexes and indicate weak antiferromagnetic interaction between the magnetic centers. The magnetic behavior of Co(II) complexes is characteristic for cobalt(II) system with an important orbital contribution via spin-orbit coupling.     

Spectroscopic and structural characteristics of Langmuir-Blodgett films of bis[2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyaninato] rare earth complexes

The monolayer behavior of bis[2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyaninato] rare earth complexes M[Pc(OC₈H₁₇)₈]₂ (M = Eu, Dy, Er) at the air-water interface and their ordered molecular assemblies fabricated by Langmuir-Blodgett technique have been investigated by a series of techniques including surface pressure-area isotherms, electronic absorption spectra, polarized absorption spectra, low-angle X-ray diffraction patterns, and transmission electron microscope (TEM). The results indicated that bis(phthalocyaninato) rare earth molecules form well-ordered stable monolayers with a face-to-face configuration and edge-on arrangement to the water surface at the air-water interface and lamellar multilayers on solid substrates. The orientation angle of phthalocyanine rings with respect to the quartz plate surface in the Langmuir-Blodgett films has been determined to be 64.6°, 63.5°, and 63.3° for the Eu, Dy, and Er double-decker complexes, respectively, by the polarized absorption spectroscopy. High-resolution TEM reveals that a series of well-ordered rodlike aggregates of bis(phthalocyaninato) rare earth complexes, which can be considered as molecular cable arrays, were formed by self-organization in the monolayers.     

Highly effective H2/D2 separation in a stable Cu-based metal-organic framework

A three-dimensional copper metal-organic framework with the rare chabazite(CHA)topology namely FJI-Y11 has been constructed with flexibly carboxylic ligand 5,5'-[(1,4-phenylenebis(methylene))bis(oxy)]diisophthalic acid(H₄L).FJI-Y11 exhibits high water stability with the pH range from 2 to 12 at temperature as high as 373 K.Importantly,FJI-Y11 also shows high efficiency of hydrogen isotope separation using dynamic column breakthrough experiments under atmospheric pressure at 77 K.Attributed to its excellent structural stability,FJI-Y11 possesses good regenerated performance and maintains high separation efficiency after three cycles of breakthrough experiments.     

Efficient white organic electroluminescent devices consisting of blue- and red-emitting layers

We report the fabrication and the characterization of white-organic-light-emitting devices consisting of a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi) and a red-emitting layer of 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-8-yl)vinyl]-4H-pyran (DCM2) doped into either 4,4′bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (α-NPD) or tris(8-hydroxyquinoline) aluminum (Alq₃). The spectral emission depends on both the doping location of DCM2 and its doping concentration. The electroluminescence (EL) spectra consist of two broad bands around 460 nm (DPVBi) and 560 nm (α-NPD:DCM2) or 590 nm (Alq₃:DCM2). We obtained an efficient white-light emission from the devices with the 0.2% DCM2 doping in α-NPD layer. The device shows the CIE coordinates of (0.33, 0.36), an external quantum efficiency (QE) of about 3.1%, and a luminous efficiency of 3.75 lm/W at luminance 100 cd/m². The maximum luminance of about 41,000 cd/m² was obtained.     

A Twisted Thieno[3,4‐b]thiophene‐Based Electron Acceptor Featuring a 14‐π‐Electron Indenoindene Core for High‐Performance Organic Photovoltaics

With an indenoindene core, a new thieno[3,4‐b ]thiophene‐based small‐molecule electron acceptor, 2,2′‐((2Z,2′Z)‐((6,6′‐(5,5,10,10‐tetrakis(2‐ethylhexyl)‐5,10‐dihydroindeno[2,1‐a]indene‐2,7‐diyl)bis(2‐octylthieno[3,4‐b]thiophene‐6,4‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile ( NITI ), is successfully designed and synthesized. Compared with 12‐π‐electron fluorene, a carbon‐bridged biphenylene with an axial symmetry, indenoindene, a carbon‐bridged E ‐stilbene with a centrosymmetry, shows elongated π‐conjugation with 14 π‐electrons and one more sp³ carbon bridge, which may increase the tunability of electronic structure and film morphology. Despite its twisted molecular framework, NITI shows a low optical bandgap of 1.49 eV in thin film and a high molar extinction coefficient of 1.90 × 10⁵m ^?1 cm^?1 in solution. By matching NITI with a large‐bandgap polymer donor, an extraordinary power conversion efficiency of 12.74% is achieved, which is among the best performance so far reported for fullerene‐free organic photovoltaics and is inspiring for the design of new electron acceptors.     

High‐Performance As‐Cast Nonfullerene Polymer Solar Cells with Thicker Active Layer and Large Area Exceeding 11% Power Conversion Efficiency

In this work, a nonfullerene polymer solar cell (PSC) based on a wide bandgap polymer donor PM6 containing fluorinated thienyl benzodithiophene (BDT‐2F) unit and a narrow bandgap small molecule acceptor 2,2′‐((2Z,2′Z)‐((4,4,9,9‐tetrahexyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IDIC) is developed. In addition to matched energy levels and complementary absorption spectrum with IDIC, PM6 possesses high crystallinity and strong π–π stacking alignment, which are favorable to charge carrier transport and hence suppress recombination in devices. As a result, the PM6:IDIC‐based PSCs without extra treatments show an outstanding power conversion efficiency (PCE) of 11.9%, which is the record value for the as‐cast PSC devices reported in the literature to date. Moreover, the device performances are insensitive to the active layer thickness (≈95–255 nm) and device area (0.20–0.81 cm²) with PCEs of over 11%. Besides, the PM6:IDIC‐based flexible PSCs with a large device area of 1.25 cm² exhibit a high PCE of 6.54%. These results indicate that the PM6:IDIC blend is a promising candidate for future roll‐to‐roll mass manufacturing and practical application of highly efficient PSCs.     

Studies on Cobalt(II) Complexes with Benzenesulfonate: Synthesis,Crystal Structure,and Spectroscopic and Magnetic Properties

Two novel transition metal benzenesulfonate complexes with a formula [Co(H₂O)₆][C₇H₅O₃SO₃]₂?2H₂O (1) and Na₄[Co(H₂O)₂ Cl₄][C₇H₅O₃SO₃]₂?4H₂O (2), have been synthesized and characterized by single-crystal X-ray diffraction technique; thermal analysis was done and spectroscopic and magnetic properties were studied. The [Co(H₂O)₆][C₇H₅O₃SO₃]₂?2H₂O (1) complex crystallizes in the triclinic system; however, the (2) complex crystallizes in the monoclinic crystal system with the C2/c space group. Each Co(II) atom in (1) and (2) is octahedrally coordinated. A hydrogen bond links the complex cation and anion, forming one-dimensional hydrogen-bonded supramolecular chains. The complexes exhibit different decomposition characteristics. Magnetic susceptibility measurement shows that complexes have weak anti-ferromagnetic intermolecular interactions between many local spins. The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures, and they are compared with those reported for related systems. Magnetic moments of both compounds at room temperature are characteristic of high-spin complexes Co(II).     

Spectroscopic,thermal and biological studies of coordination compounds of sulfasalazine drug: Mn(II), Hg(II), Cr(III), ZrO(II), VO(II) and Y(III) transition metal complexes

The complexations of sulfasalazine (H₃Suz) with some of transition metals have been investigated. Three types of complexes, [Mn(HSuz)⁻²(H₂O)₄]·2H₂O, [M(HSuz)⁻²(H₂O)₂]·xH₂O (M = Hg(II), ZrO(II) and VO(II), x = 4, 8 and 6, respectively) and [M(HSuz)⁻²(Cl)(H₂O)₃]·xH₂O (M = Cr(III) and Y(III), x = 5 and 6, respectively) were obtained and characterized by physicochemical and spectroscopic methods. The IR spectra of the complexes suggest that the sulfasalazine behaves as a monoanionic bidentate ligand. The thermal decomposition of the complexes as well as thermodynamic parameters (δE*, δH*, δS* and δG*) were estimated using Coats-Redfern and Horowitz-Metzger equations. In vitro antimicrobial activities of the H₃Suz and the complexes were tested.     

A novel preparation method for porous noble metal/ceramic catalytic membranes

Adsorption at liquid/solid interface has been explored to prepare catalytically active ceramic membranes. Boehmite sol maintains its dynamic stability in the pH range of 3.5–4. Adsorption of metal salt on the sol particles can only be performed in the above pH range, but the adsorption can still be optimized by proper choice of ligand. Therefore, the effect of the ligands (NH₃, Cl^–, EDTA) on the adsorption of the noble metal ions (Pd(II), Pt(II), Pt(IV) and Rh(III)) as a function of pH on -Al₂O₃ particles was studied. Thus the noble metal complexes which can significantly adsorb in the above pH range were found. Using the complexes, the noble metal ion modified boehmite sols were synthesized. Then by the sol-gel process, the porous noble metal/ceramic cataytic membranes were prepared. The membranes were further characterized by N₂ adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and SEM-WDX (wave dispersion of X-ray). The H₂ and N₂ permeation through these membranes at elevated temperatures was also measured. Based on the above experiments, the novel technique can produce the mesoporous catalytically active ceramic membranes without any defects and with a uniform dispersion of the active materials in the coating.     

Ternary Nonfullerene Polymer Solar Cells with 12.16% Efficiency by Introducing One Acceptor with Cascading Energy Level and Complementary Absorption

A novel small‐molecule acceptor, (2,2′‐((5E,5′E)‐5,5′‐((5,5′‐(4,4,9,9‐tetrakis(5‐hexylthiophen‐2‐yl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(4‐(2‐ethylhexyl)thiophene‐5,2‐diyl))bis(methanylylidene)) bis(3‐hexyl‐4‐oxothiazolidine‐5,2‐diylidene))dimalononitrile (ITCN), end‐capped with electron‐deficient 2‐(3‐hexyl‐4‐oxothiazolidin‐2‐ylidene)malononitrile groups, is designed, synthesized, and used as the third component in fullerene‐free ternary polymer solar cells (PSCs). The cascaded energy‐level structure enabled by the newly designed acceptor is beneficial to the carrier transport and separation. Meanwhile, the three materials show a complementary absorption in the visible region, resulting in efficient light harvesting. Hence, the PBDB‐T:ITCN:IT‐M ternary PSCs possess a high short‐circuit current density (J_sc) under an optimal weight ratio of donors and acceptors. Moreover, the open‐circuit voltage (V_oc) of the ternary PSCs is enhanced with an increase of the third acceptor ITCN content, which is attributed to the higher lowest unoccupied molecular orbital energy level of ITCN than that of IT‐M, thus exhibits a higher V_oc in PBDB‐T:ITCN binary system. Ultimately, the ternary PSCs achieve a power conversion efficiency of 12.16%, which is higher than the PBDB‐T:ITM‐based PSCs (10.89%) and PBDB‐T:ITCN‐based ones (2.21%). This work provides an effective strategy to improve the photovoltaic performance of PSCs.     

Characterization of aqueous and solid inclusion complexes of diuron and isoproturon with beta-cyclodextrin

The interaction of diuron and isoproturon herbicides with beta-cyclodextrin is conducive to the formation of inclusion compounds in aqueous solution as well as in the solid state. The physico-chemical study of these complexes was carried out by various analytical techniques such as ultraviolet (UV), Fourier transform infrared (FT-IR), Raman, X-ray diffraction, and 1H-NMR (nuclear magnetic resonance) spectroscopies. The existence of inclusion complexes in water solution between the beta-cyclodextrin and each of the herbicides was revealed by electronic absorption and 1H-NMR spectroscopies. A 1:1 stoichiometry was determined for both complexes in aqueous medium from UV absorption spectra by using the Benesi-Hildebrand method; the relative stability constants at room temperature were calculated at 2700 +/- 300 L mol(-1) and 750 +/- 50 L mol(-1) for isoproturon and diuron, respectively. In the solid state, inclusion processes with beta-cyclodextrin were characterized by means of infrared and Raman techniques and confirmed by X-ray diffraction spectra.     

Synthesis and spectral studies on some 3d metal complexes of a mesogenic ligand,N-(4′′′-n-butylphenyl)-4-(4′-hexyloxybenzoate)salicylaldimine

A mesogenic (nematic) Schiff's base, N-(4′′′-n-butylphenyl)-4-(4′-hexyloxy benzoate)salicylaldimine, Hbphbsal, (abbreviated as HL¹), was synthesized and its structure studied by elemental analyses, mass, NMR and IR spectra. A series of mesogenic/non-mesogenic 3d metal complexes of the general formula, [M(L¹)₂]_n where M^II = Mn, Co, Ni, Cu and Zn has been prepared and structures were studied by various spectroscopic techniques. Spectral studies imply coordination of the ligand (HL¹) as uni-negative bi/tri-dentate species to the metal ions, rendering overall geometry to distorted square planar (in case of Cu^II complex) and octahedral geometry. The ESR spectra confirmed the presence of mixed copper–nitrogen and oxygen bonds in the chelate based on the g_?? value. The Cu^II, Co^II and Ni^II complexes were found to be mesogenic (nematic) and their transition, melting and clearing points deviated from the ligand upon complexation.     

Effect of Annealing Conditions in Hydrogen Atmosphere on Structural,Optical and Magnetic Properties of Nanocrystalline CdO Codoped with Cu and Co Ions for DMS Applications

Cadmium oxide powder codoped with Cu and Co ions (Cd_0.94Cu_0.01Co_0.05O) was synthesised by thermal co-decomposition of a mixture of cadmium acetate dihydrate, bis(acetylacetonato)copper(II) and bis(acetylacetonato)cobalt(II) complexes. The purpose of the present investigation is to study the effect of H₂-annealing conditions on the evolution of structure, optical and magnetic properties by varying temperature (300, 350 and 400 °C) and duration time (30 and 60 min). X-ray fluorescence (XRF) and X-ray diffraction (XRD) methods confirm the purity and the formation of single nanocrystalline phase of the as-prepared powder; thus, both Cu and Co ions were incorporated into CdO lattice, forming solid solutions. Magnetic measurements reveal that the as-prepared solid solution (SS) gained paramagnetic (PM) properties, although pure CdO itself is considered as diamagnetic (DM). The measured effective magnetic moment of doped Co²⁺ was 3.55 μ _B. Interestingly, it was found that the hydrogenation process could transform the properties of the SS into room-temperature ferromagnetic (RT-FM) only. For example, the coercivity (H _c), remanence (M _r) and saturation magnetisation (M _s) were 279 Oe, 0.187 emu/g and 1.739 emu/g, respectively for SS annealed in H₂ gas at 350 °C for 30 min. Thus, the possibility of producing CdO with RT-FM was proved, where the magnetic characteristics were tailored by doping and post treatment under H₂ gas, thereby a new potential candidate to be used as a dilute magnetic semiconductor (DMS). However, the real effect of H₂ annealing on such drastic transformation in the magnetic behaviour needs some in-depth theoretical research work.     

Study of magnetic properties of two samples from FeVO<Subscript>4</Subscript>-Co<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> system

Two samples containing phases formed in the FeVO₄-Co₃V₂O₈ system were prepared by a conventional sintering method. The sample designated as H5 was one-phase with the howardevansite-type structure, while the sample designated as HL7 contained a mixture of H-type and lyonsite-type structures. The temperature dependence of the electron paramagnetic resonance (EPR) spectra and static magnetic susceptibility χ was investigated in the temperature range from liquid helium to room temperature. Both the EPR spectra and the dc magnetic susceptibility showed anomalous behavior indicating that the magnetic competition process may be responsible. A comparison of the obtained results with previous studies on related compounds with the same structure, i.e. M₃Fe₄V₆O₂₄ (M = Mg(II), Zn(II), and Cu(II)) revealed that the observed anomaly shifted to lower temperatures on replacing the non-magnetic ions by magnetic Co(II) ions. The temperature dependence of the inverse susceptibility χ ^?1 indicates the existence of antiferromagnetic interactions between Fe(III) and Co(II) spins in sample H5. The obtained values of the Curie-Weiss temperatures are lower than for the Mn₃Fe₄V₆O₂₄ compound and comparable to compounds from M₃Fe₄V₆O₂₄ systems with M diamagnetic cations. The introduction of cobalt cations intensifies the magnetic frustration what is reflected in the temperature dependence of the magnetic susceptibility at low temperatures.