Growth and optical properties of transition metal oxides single crystal solid solutions
Abstract NiO, CoO, MnO single crystals and single crystal solid solutions of Ni c Mg 1− c O, Co c Mg 1− c O and Mn c Mg 1− c O were grown by the method of chemical transport reaction (the “sandwich” technique). The nature of the observed absorption and luminescence bands is explained in terms of the electronic transition of bivalent nickel, cobalt and manganese. The fine structure of the observed bands in NiO and MnO are connected to the pure exciton transition and to the exciton-magnon excitation.
X-ray absorption spectroscopy study of NicMg1-cO solid solutions on the Ni K edge
We present an X-ray absorption spectroscopy study of NicMg1-cO (0.01<or=c<or=1) solid solutions on the Ni K edge. The analysis of XANES and EXAFS regions allowed us to obtain the following results. The nickel ions are located in a distorted environment and shift upon dilution to the off-centre positions. In the first shell, the average Ni-O distance increases linearly upon dilution. In the second shell, the average Ni-Ni distance remains unchanged and decreases slightly at low nickel concentration while the dependence of the average Ni-Mg distance has a break at c approximately=0.6 and is nearly constant below and above this concentration which corresponds to the point of antiferromagnetic-paramagnetic phase transition. The number of nickel and magnesium ions in the second shell of nickel ions varies in agreement with the random distribution model. The results obtained are discussed in comparison with the ones from X-ray diffraction, optical spectroscopy and magnetic measurements.
Farbe und Konstitution bei anorganischen Feststoffen. II. Die Lichtabsorption des zweiwertigen Nickels in oxydischen Koordinationsgittern
Durch spektralphotometrische Bestimmung der Remission von Pulvern wurde die Abhangigkeit der Lichtabsorption des Ni2+ von folgenden Faktoren untersucht: 1. Koordinationszahl (Ni0,1Mg0,9Al2O4, KZ = 4, Ni0,1Mg0,9O, KZ = 6) 2. Gitterdehung (Ni0,1Mg0,9Al2O4 Ni0,1Mg0,9Ga2O4), (Ni0,1Mg0,9O Ni0,01Mg0,69Zn0,3O), (Ni0,1Mg0,9TiO3 Ni0,1Cd0,9TiO3) 3. Symmetrieerniedrigung bzw. Verzerrung des Koordinationspolyeders (Ni0,1Zn1,9SiO4, Ni0,01Zn0,99O), (Ni0,25Mg1.75SiO4, Ni0,1Mg0,9TiO3). Wie im Fall des Co2+ bewirkt hier die Erhohung der Koordinationszahl von 4 auf 6 bei einer Eigensymmetrie des Koordinationspolyeders Td bzw. Oh eine UV-Verschiebung der Hauptabsorptionsbanden. Eine Gitterdehnung kann, insbesondere bei einfachen Gittern, eine Rotverschiebung bewirken. Eine Erniedrigung der Punktsymmetrie des Koordinationspolyeders hat nur dann eine starkere Rotverschiebung und Erhohung der Absorptionsintensitat zur Folge, wenn damit gleichzeitig eine starkere Verzerrung des Koordinationsoktaeders verbunden ist. Das System Zn2SiO4/Ni2SiO4 wurde spektralphotometrisch untersucht und die Grenzen der Homogenitatsgebiete aus dem Vergleich der Spektren ermittelt. 
 
 
 
The influence of coordination number, lattice expansion, and decreasing degree of symmetry or distortion of the coordination polyhedron on the light absorption of Ni2+-ions in various oxides (see „Inhaltsubersicht°”) have been studied by spectrophotometric determination of powder remission. 
 
 
 
As in the case of Co(II)-containing oxides, the main absorption band is shifted toward the UV-region by raising the coordination number from 4 to 6. Displacement toward the red sometimes occurs on lattice expansion. 
 
 
 
Stronger shiftings to the red and high intensities of absorption have been observed when the decrease of point symmetry of coordination polyhedron is accompanied by stronger distortion. 
 
 
 
The ranges of homogeneity in the system Zn2SiO4/Ni2SiO4 have been determined spectrometrically.