Transport and Magnetic Studies of New Mixed-Valence Compounds: K3Cu8Se6, KCu3Se2, K3Cu8Te6 and BaCuS3-x

New mixed-valent copper chalcogenides BaCuS3_x and K3Cu8X6 with X = Se or Te and KCu3Se2, with chemical patterns corresponding to the recently investigated K3Cu8S6 and KCu3S2, were synthesized. For these new samples the results of resistivity and magnetic susceptibility measurements are presented. For BaCuS3_x, K3Cu8Se6 and KCu3Se2 the metal—insulator transition is observed with the low temperature phase being metallic, which is untypical, whereas K3Cu8Te6 is a metal in the investigated temperature range. The temperature dependence of magnetic susceptibility of the studied samples testifies to their diamagnetic or weakly paramagnetic behaviour

Electric Properties of a New Ferrite K4Cu2Fe7V7O32 with a Hollandite-Type Structure

Results of investigation of electric transport properties of a new magnetically ordered hollandite compound with a composition K4Cu2Fe7V7O32 will be reported. Resistance versus temperature measurements (78-350 K) on the ceramic samples were carried out by means of four-lead dc, pulse and ac techniques. The temperature coefficient of resistance determined from R(T) measured by dc and pulse techniques has been found to be zero in 78-200 K range and it takes negative values in temperatures above 200 K. Additionally, hysteresis effect was observed in temperature range 200-310 K. Details of relationship between the resistance R and voltage U at different temperatures will be discussed. Surprisingly enough, the R(T) dependence of studied compound bears a characteristic features for amorphous material although the crystallinity of our samples has been confirmed by XRD and Mössbauer spectroscopy

Magnetic domain behaviour of Cu-ferrite doped with small quantities of Cd or Be ions

The temperature dependences of the ac-initial susceptibility Xac(T) of a Cu1-xMexFe2O4 ferrospinel system with Me = Cd/Be (size effect) and x = 0.05 were performed in 300 - 1100 K range. A remarkable thermal treatment cycling effects were observed. The tamperatures of blocking effect, Hopkinson effect, spontaneous spin-reorientation phase transition and Curie temperature were determined. The irreversible magnetic domain behaviour of Cu-Cd/Be ferrite system with single domain and multidomain particles were explained on the basis of cooperative Jahn-Teller effect (accompanied by ionic diffusion), magnetic anisotropy of this system and properties of magnetic particles

XPS Study of "infinite Chain" Ca2\text{}_{2}CuO3\text{}_{3} and Ca0.5\text{}_{0.5}Sr0.5\text{}_{0.5}CuO2\text{}_{2} Compounds

Al K$\text{}_{α}$ excited photoelectron spectra (X-ray photoelectron spectroscopy) of the O 1s, Cu 2p, Ca 2p, Sr 3d core levels were measured for "infinite chain" Ca$\text{}_{2}$CuO$\text{}_{3}$ and Ca$\text{}_{0.5}$Sr$\text{}_{0.5}$CuO$\text{}_{2}$ compounds. The analysis indicates that for Ca$\text{}_{2}$CuO$\text{}_{3}$ the surface electronic structure is strongly influenced by a humid atmosphere. The surface layer is formed predominantly by copper hydroxide. The minor features of Cu 2p and O 1s are characteristic of the bulk bonding states. The valences of the Cu, Ca, and Sr atoms are close to 2+. The core electron binding energies (≈ 934 eV peak) are due to the 2p$\text{}_{3}\text{}_{/}\text{}_{2}$ 3d$\text{}^{10}$L$\text{}^{1}$ configuration of Cu(II) ions in the square planar coordination for both samples

IR Studies of the Phase Transformation of Fe2O3 → Fe3O4by Magnetomechanical Activation

The phase transformation of hematite αFe2O3 into magnetite Fe3O4 during wet milling in vacuum as a result of mechanochemical process has been investigated by infrared spectroscopy. The FTIR spectra were recorded in the wavenumber range kom 400 to 4000 cm-1. Two very strong bands were generally observed : one in the range 557-577cm-1 with shoulders in 632-693 cm-1, the other at about 475 cm-1. The most important feature is a very strong dependence of the intensities of the main absorption bands on the milling time of the sample. In addition, there was a broad band in the 3000-3700 cm-1 region related to the appearance of a certain number of OH groups in the spinel lattice. The results are discussed assuming the theoretically indicated active IR modes for ferites. A little disorded was interpreted as generated by ball milling and no traces of amorphization were observed

Transport and Magnetic Studies of New Mixed-Valence Compounds: K3\text{}_{3}Cu8\text{}_{8}Se6\text{}_{6}, KCu3\text{}_{3}Se2\text{}_{2}, K3\text{}_{3}Cu8\text{}_{8}Te6\text{}_{6} and BaCuS3−x\text{}_{3-x}

New mixed-valent copper chalcogenides BaCuS$\text{}_{3-x}$ and K$\text{}_{3}$Cu$\text{}_{8}$X$\text{}_{6}$ with X=Se or Te and KCu$\text{}_{3}$Se$\text{}_{2}$, with chemical patterns corresponding to the recently investigated K$\text{}_{3}$Cu$\text{}_{8}$S$\text{}_{6}$ and KCu$\text{}_{3}$S$\text{}_{2}$, were synthesized. For these new samples the results of resistivity and magnetic susceptibility measurements are presented. For BaCuS$\text{}_{3-x}$, K$\text{}_{3}$Cu$\text{}_{8}$Se$\text{}_{6}$ and KCu$\text{}_{3}$Se$\text{}_{2}$ the metal-insulator transition is observed with the low temperature phase being metallic, which is untypical, whereas K$\text{}_{3}$Cu$\text{}_{8}$Te$\text{}_{6}$ is a metal in the investigated temperature range. The temperature dependence of magnetic susceptibility of the studied samples testifies to their diamagnetic or weakly paramagnetic behaviour

Delocalization of the Cu 2+

Supertransferred hyperfine interactions between the $Cu^{2+}$ unpaired electron and the $\text{}^{105}Pd$ nuclei in the $Sr_2Pd_{0.99}Cu_{0.01}O_3$ ceramic were studied by the EPR method. The spectrum of isolated -Pd-O-$CuO_2$-O-Pd- units ($g_∥$ = 2.280±0.001; $g_⊥$ = 2.040±0.001; $A_∥(\text{}^{63}Cu)$ = 13 mT±0.1; $A_∥(\text{}^{65}Cu)$ = 13.9 ±0.1 mT; $A_⊥(\text{}^{63,65}Cu)$ = 0.0 mT) overlaps the signal from small groups of exchange coupled $Cu^{2+}$ ions ($g_∥$ = 2.278±0.002; $g_⊥$ = 2.041±0.001). The isotropic contribution was shown to dominate in the Cu-Pd supertransferred interactions ($A_∥(\text{}^{105}Pd) = A_⊥ (\text{}^{105}Pd)$ = 1 mT = $a_\text{iso}$ Pd)

Delocalization of the Cu2+Cu^{2+} Unpaired Electron on the Next Nearest Ligands in Sr2Pd0.99Cu0.01O3Sr_2Pd_{0.99}Cu_{0.01}O_3 Ceramics

Supertransferred hyperfine interactions between the $Cu^{2+}$ unpaired electron and the $\text{}^{105}Pd$ nuclei in the $Sr_2Pd_{0.99}Cu_{0.01}O_3$ ceramic were studied by the EPR method. The spectrum of isolated -Pd-O-$CuO_2$-O-Pd- units ($g_∥$ = 2.280±0.001; $g_⊥$ = 2.040±0.001; $A_∥(\text{}^{63}Cu)$ = 13 mT±0.1; $A_∥(\text{}^{65}Cu)$ = 13.9 ±0.1 mT; $A_⊥(\text{}^{63,65}Cu)$ = 0.0 mT) overlaps the signal from small groups of exchange coupled $Cu^{2+}$ ions ($g_∥$ = 2.278±0.002; $g_⊥$ = 2.041±0.001). The isotropic contribution was shown to dominate in the Cu-Pd supertransferred interactions ($A_∥(\text{}^{105}Pd) = A_⊥ (\text{}^{105}Pd)$ = 1 mT = $a_\text{iso}$ Pd)

The Origin of EPR Signals in SrCuO2\text{}_{2} Ceramics

The origin and thermal evolution of the EPR signals in SrCuO$\text{}_{2}$ ceramics are studied. It has been shown that the EPR signals observed in this ceramic material are due to contamination with other phases. The axial signal is due to SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O, which is a product of water reactions with SrCuO$\text{}_{2}$