Electrical and optical properties of high-purity p-type single crystals of GeFe2O4

Single crystals of the spinel GeFe₂O₄, grown by the chemical vapor transport technique, are p-type semiconductors with an acceptor ionization energy of 0.39 eV. The material is a heavily compensated band-type semiconductor, with a typical hole concentration of 10¹⁴ cm^?3 near room temperature, and a temperature-independent Hall mobility of 2 cm²/V·sec. Optical absorption measurements show the optical band gap to be ?2.3 eV; the octahedral field splitting of the Fe²⁺d-levels is 10 200 cm^?1. Magnetic measurements show that n_eff is 5.26, from which a trigonal field splitting of 950 cm^?1 is derived.     

The crystal structure of Cu4(PO4)2O

Cu₄(PO₄)₂O crystallizes in the space group $\text{P}\text{1}$ with a = 7.5393(8) Å, b = 8.1021(9) Å, c = 6.2764(8) Å, α = 113.65(1)°, β = 98.42(1)° and γ = 74.19(1)°. The structure was refined by full-matrix least-squares techniques using automatic diffractometer data to R = 0.046 (R_w = 0.056). Four unique copper atoms are in six, five-, and four-coordinated polyhedra which are linked together to form a three-dimensional network. The structure is best described in terms of a cubic close-packed array of oxygen atoms with one-tenth of the possible anion sites vacant.     

Growth and characterization of n-WS2 and niobium-doped p-WS2 single crystals

Single crystals of n- and p-WS₂ were obtained by chemical vapor transport using chlorine and bromine as transporting agents. The best niobium-doped WS₂ crystals were obtained when the concentration of the charge (formulated (1 ? x)WS₂ · (x)NbS₂) was ? 37 mg charge/ml of tube, and x = 0.01 to 0.03. A thermodynamic analysis of the crystal growth process is consistent with the observed doping concentration and other properties of the crystals obtained by this process. The crystals grown are characterized by electrical transport and surface photovoltage measured capacitance techniques.     

Preparation and electronic properties of MoS2 and WS2 single crystals grown in the presence of cobalt

Single crystals of MoS₂ and WS₂ were grown by chemical vapor transport in both the presence and absence of cobalt. Hall measurements indicate that cobalt cannot diffuse appreciably into the bulk of MoS₂ or WS₂ and, therefore, can be present only on the surface. Similar results were obtained for as-grown crystals annealed or sulfided in contact with Co₉S₈ or sulfided after being dipped in a 0.1M CoSO₄/methanol solution.     

Ca7Au3 and Ca5Au4, two structures closely related to the Th7Fe3 and Pu5Rh4 types

Two new intermetallic compounds have been synthetized and structurally studied by single crystal diffractometric data: Ca₇Au₃ (oP80, space groupPbca,a = 20.742(8), b = 18.036(8), c = 6.665(2) A?,Z = 8, R = 0.051) and Ca₅Au₄ (mP18, space groupP2₁/c, a = 8.028(3), b = 8.019(6), c = 7.727(3) A?, β = 109.16(6)°,Z = 2, R = 0.104). Both atomic arrangements, which represent new structural types, are based on Au-centered Ca trigonal prisms and are geometrically related to the Th₇Fe₃ and Pu₅Rh₄ structures.     

Preparation and properties of PdPSe single crystals

Single crystals of PdPSe were shown to be n-type semiconductors. Weak Pauli paramagnetic behavior was observed, which is consistent with the presence of delocalized electrons. Electrical measurements showed a room-temperature resistivity ? = 70 ohm-cm, activation energy of resistivity E_a = 0.32 eV, and Hall mobility μ = 34 cm² V^?1 sec^?1. Photoelectronic measurements in aqueous solutions of $\text{I}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}{}_3$ indicate that PdPSe has high quantum efficiencies below 800 nm. The indirect optical band gap is 1.28(2) eV.     

Heat capacity and thermodynamic functions of MnBr2 · 4D2O and MnCl2 · 4D2O

The heat capacities of MnBr₂ · 4D₂O and MnCl₂ · 4D₂O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°_TH°₀) and S°_T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl₂ · 4D₂O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K.     

Thermodynamics of Sr(NO3)2 and Cd(NO3)2 in mixed solvents from viscosity data

The viscosities of Sr(NO₃)₂ and Cd(NO₃)₂ have been determined in dioxane, glycol and methyl alcohol+water mixtures at 10, 20 and 30% by weight. The B values have been computed at different temperatures both from the Jones—Dole and Das's equation. From the B values, the effective rigid molar volume, its change with % of organic solvent, temperature and the ion—solvent interaction have been inferred. Activation parameters have also been calculated and the structure breaking effect has been deduced.     

Thermodynamics of Sr(NO3)2 and Cd(NO3)2 in aquo-organic solvents from conductance data

The ion-solvent interaction of Sr(NO₃)₂ and Cd(NO₃)₂ in 10, 20 and 30 wt.% organic solvent (dioxane, glycol, methyl alcohol)-water mixtures at different temperatures has been studied using electrolytic conductivity data. The dissociation constant of the ion-pair Sr(NO₃)⁺ and Cd(NO₃)⁺ has been calculated along with ΔG⁰_t, ΔG⁰_t(cl) and ΔG⁰_t(ch). The ion pairs interact with the solvents and the interaction is of the order dioxane+water>methyl alcohol+water>glycol+water.     

Preparation and photoelectronic properties of the system Cd2Ge1−xSixO4

Members of the system Cd₂Ge_1?xSi_xO₄ where 0 ≤ x ≤ 0.4 have been prepared. These compounds were observed to crystallize with the olivine structure, space group Pbnm. The resistivity, Hall mobility, flat-band potential, band gaps, and stability were determined as functions of composition. The variation of these photoelectronic properties can be attributed to the reduction of the cell parameters with increasing silicon substitution. The substitution of silicon for germanium reduces the loss of photocurrent from 25% after 1 hr for x = 0.0 to only 6% after 22 hr for x = 0.4.     

Preparation and properties of the system Fe1−xVxNbO4

Members of the system Fe_1?xV_xNbO₄ were prepared and their crystallographic, electrical, and magnetic properties were determined. The wolframite structure is formed for x ≤ 0.2, but for x ≥ 0.4, a phase transformation to the rutile structure takes place. Magnetic studies established the formal valencies of the elements for members crystallizing with the wolframite phase. However, similar analyses of compounds with the rutile structure did not provide a unique assignment of the formal valencies.     

Preparation and comparison of the photoelectronic properties of Sr2Nb2O7 and Ba0.5Sr0.5Nb2O6

The two alkaline earth niobates Sr₂Nb₂O₇ and Ba_0.5Sr_0.5Nb₂O₆ have been prepared, their electronic properties measured, and their photoresponses compared. The indirect band gap in Sr₂Nb₂O₇ is 3.86 eV compared with 3.38 eV for Ba_0.5Sr_0.5Nb₂O₆. Hence, photoanodes composed of Sr₂Nb₂O₇ respond to much less of the “white” light spectrum than those made from Ba_0.5Sr_0.5Nb₂O₆. Nevertheless, their electrical outputs at an anode potential of 0.8 eV with respect to SCE in 0.2 M sodium acetate under “white” xenon arc irradiation of 1.25 W/cm² are comparable.     

Preparation and properties of the system Fe1−xCrxNbO4

Members of the system Fe_1?xCr_xNbO₄ were prepared and their magnetic and electronic properties were investigated. It was shown that chromium substitution favored the formation of the rutile structure, which resulted in a decrease in the electrical conductivity because of randomization of the transition metal ions in the structure. The replacement of a few percent of Fe³⁺ with Cr³⁺ caused a significant lowering of the lowest optical band gap, whereas the higher-energy transitions remained essentially unchanged. This resulted in increased response to the longer wavelengths of the solar spectrum.     

Optical and ESR investigations of lanthanum aluminates LaMg1−xMnxO19 single crystals with magnetoplumbite-like structure

New lanthanum aluminates LaMAl₁₁O₁₉ (M²⁺ = Ni, Co, Mn, Mg_1?xMn_x, 0 ≤ x ≤ 1), with magnetoplumbite-like structure have been obtained as single crystals. This paper is particularly devoted to the Mn²⁺ and $\text{Mg}{}^{\mathrm{2+}}\text{Mn}{}^{\mathrm{2+}}$ mixed compounds, which exhibit promising luminescent properties. Several characteristics of the crystals are given. The absorption spectra of the materials, as grown, are assigned to Mn²⁺ ions in tetrahedral sites. After annealing in air new absorptions attributed to octahedral Mn³⁺ ions, appear. The ESR spectra of Mn²⁺ in all these crystals exhibit axial symmetry. For x ≤ 0.25 they arise from isolated Mn²⁺ ions in slightly distorted tetrahedral sites and reveal a strong disorder effect. For x ≥0.5 the spectra consist of a single line, attributed to clusters of magnetically interacting Mn²⁺ ions.     

Isothermal differential scanning calorimetry on an exothermic phenomenon during thermal decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O

An exothermic phenomenon and a simultaneous rapid evolution of a small amount of carbon dioxide at ?500°C during thermal decomposition of hydromagnesite 4 MgCO₃ · Mg(OH)₂ · 4 H₂O was studied by isothermal DSCTG in a carbon dioxide atmosphere. It was quantitatively confirmed that the exothermic phenomenon was due to crystallization of MgCO₃ from the amorphous phase and that the evolution of carbon dioxide was due to decomposition of the MgCO₃ by the heat of crystallization (?3.4 kcal mole^?1.     

Normal modes of the MoO2−4 ion in Tb1.8Eu0.2(MoO4)3 single crystal

Polarized Raman spectra (single crystal) at 300 K and infrared spectra (powder) at 300 and 77 K in the region 250–1000 cm^?1 of a binary molybdate of terbium and europium have been recorded. Based on C_2v symmetry, group theoretical analysis has been carried out and a vibrational assignment is proposed.     

Infrared spectra of KNaSO4 and K3Na(SO4)2

The infrared spectra, transmittance and polarized reflectance, of KNaSO₄ and K₃Na(SO₄)₂ are reported. Group theoretical analysis was carried out and a vibrational assignment proposed on basis of C_3v and D_3d symmetries. Factor group and site effects are discussed.     

Survey of the phase formation in the Yb2O3Ga2O3MO and Yb2O3Cr2O3MO systems in air at high temperatures (M: Co,Ni, Cu,and Zn)

The phase relations in the Yb₂O₃Ga₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃CuO system at 1000°C and the Yb₂O₃Ga₂O₃ZnO system at 1350 and 1200°C, the Yb₂O₃Cr₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃CuO system at 1000°C, and the Yb₂O₃Cr₂O₃ZnO system at 1300 and 1200°C were determined in air by means of a classical quenching method. YbGaCoO₄ (a = 3.4165(1) and c = 25.081(2) Å), YbGaCuO₄ (a = 3.4601(4) and c = 24.172(6) Å), and YbGaZnO₄ (a = 3.4153(5) and c = 25.093(7) Å), which are isostructural with YbFe₂O₄ (space group: $\text{R}\text{3}\text{m, a = 3.455(1)}$ and c = 25.109(2) Å, were obtained as stable phases. In the Yb₂O₃Ga₂O₃NiO system and the Yb₂O₃Cr₂O₃MO system (M: Co, Ni, Cu, and Zn), no ternary stable phases existed.     

Spinel, YbFe2O4, and Yb2Fe3O7 types of structures for compounds in the In2O3 and Sc2O3---A2O3---BO systems [A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, Cu, or Zn] at temperatures over 1000°C

In the Sc₂O₃---Ga₂O₃---CuO, Sc₂O₃---Ga₂O₃---ZnO, and Sc₂O₃---Al₂O₃---CuO systems, ScGaCuO₄, ScGaZnO₄, and ScAlCuO₄ with the YbFe₂O₄-type structure and Sc₂Ga₂CuO₇ with the Yb₂Fe₃O₇-type structure were obtained. In the In₂O₃---A₂O₃---BO systems (A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, or Zn), InGaFeO₄, InGaNiO₄, and InFe³⁺MgO₄ with the spinel structure, InGaZnO₄, InGaMgO₄, and InAlCuO₄ with the YbFe₂O₄-type structure, and In₂Ga₂MnO₇ and In₂Ga₂ZnO₇ with the Yb₂Fe₃O₇-type structure were obtained. InGaMnO₄ and InFe₂O₄ had both the YbFe₂O₄-type and spinel-type structures. The revised classification for the crystal structures of AB₂O₄ compounds is presented, based upon the coordination numbers of constituent A and B cations.     

Disorder in the crystal structure of NaNi4(PO4)3

NaNi₄(PO₄)₃ crystallizes in the space group Amam, a = 9.892(1), B = 14.842(2), and c = 6.3576(2) Å. For Z = 4, the calculated density is 3.862 g/cm³ (V = 933.3ų). The presence of several weak reflections (of the class 2k0 and 6k0) which should be systematically absent in this space group has been attributed to a partial disorder of one of the phosphate tetrahedra. Two half-occupied P(2) sites related by a mirror normal to the a axis result in a column of phosphate tetrahedra pointing either up or down in this direction. Nickel atoms occupy five- and six-coordinated sites while sodium is six-coordinated.