Pavel Karen

• Karen, Pavel (2021). Synthesis and equilibrium oxygen nonstoichiometry of PrBaFe2O5+w. Journal of Solid State Chemistry. ISSN 0022-4596. 299, p. 1–8. doi: 10.1016/j.jssc.2021.122147.
• Linden, J; Lindroos, F. & Karen, Pavel (2017). Orbital occupancy evolution across spin- and charge-ordering transitions in YBaFe2O5. Journal of Solid State Chemistry. ISSN 0022-4596. 252, p. 119–128. doi: 10.1016/j.jssc.2017.04.036. Full text in Research Archive
• Karen, Pavel; McArdle, Patrick & Takats, Josef (2016). Comprehensive definition of oxidation state (IUPAC Recommendations 2016). Pure and Applied Chemistry. ISSN 0033-4545. 88, p. 831–839. doi: 10.1515/pac-2015-1204. Full text in Research Archive
• Görbitz, Carl Henrik; Karen, Pavel; Dusek, Michal & Petricek, Vaclav (2016). An exceptional series of phase transitions in hydrophobic amino acids with linear side chains. IUCrJ. ISSN 2052-2525. 3, p. 341–353. doi: 10.1107/S2052252516010472.
• Karen, Pavel (2015). Oxidation state, a long-standing issue! Angewandte Chemie International Edition. ISSN 1433-7851. 54(16), p. 4716–4726. doi: 10.1002/anie.201407561.
• Gorbitz, Carl Henrik & Karen, Pavel (2015). Twin displacive phase transitions in amino acid quasiracemates. Journal of Physical Chemistry B. ISSN 1520-6106. 119(15), p. 4975–4984. doi: 10.1021/acs.jpcb.5b01483.
• Karen, Pavel; McArdle, Patrick & Takats, Josef (2014). Toward a comprehensive definition of oxidation state (IUPAC Technical Report). Pure and Applied Chemistry. ISSN 0033-4545. 86(6), p. 1017–1081. doi: 10.1515/pac-2013-0505.
• Jantsky, Laurent; Okamoto, Hiroshi; Thomas, Michael; Karen, Pavel; Hauback, Bjørn & Rosseinsky, Matthew J [Show all 7 contributors for this article] (2014). Complex Magnetic Behavior in the PrSr3(Fe1–xCox)3O10−δ n = 3 Ruddlesden–Popper-Type Solid Solution with High Valent Cobalt and Iron. Chemistry of Materials. ISSN 0897-4756. 26(2), p. 886–897. doi: 10.1021/cm400394c.
• Lindé, Johan Kaarle Mikael; Lindroos, F. & Karen, Pavel (2014). Iron orbital occupancies upon valence mixing of charge-ordered GdBaFeIIFeIIIO5. Hyperfine Interactions. ISSN 0304-3843. 226(1-3), p. 329–339. doi: 10.1007/s10751-013-0973-8.
• Olsen, Jørn Eirik; Karen, Pavel; Sørby, Magnus Helgerud & Hauback, Bjørn (2014). Effect of chloride substitution on the order-disorder transition in NaBH4 and (NaBD4)-B-11. Journal of Alloys and Compounds. ISSN 0925-8388. 587, p. 374–379. doi: 10.1016/j.jallcom.2013.10.171. Full text in Research Archive
• Lindén, J. & Karen, Pavel (2012). Modeling hyperfine parameters observed from the charge-ordered to valence-mixed state of NdBaFe2O5. Journal of Physics: Condensed Matter. ISSN 0953-8984. 24(37). doi: 10.1088/0953-8984/24/37/376002.
• Linden, J & Karen, Pavel (2010). NdBaFe2O5+w and steric effect of Nd on valence mixing and ordering of Fe. Journal of Solid State Chemistry. ISSN 0022-4596. 183(11), p. 2703–2713. doi: 10.1016/j.jssc.2010.09.012.
• Andersson, K. Kristoffer & Karen, Pavel (2009). Mössbauer Spectroscopy in the Nordic countries; University of Oslo. Mössbauer Effect Reference and Data Journal. ISSN 0163-9587. 32(1), p. 34–36. Show summary

  Professor of Physical Biochemistry K. Kristoffer Andersson at University of Oslo (Department of Molecular Biosciences) has used Mössbauer spectroscopy to study heme and di-iron proteins since 1982. Together with Prof. Eckard Münck (University of Minnesota) he performed detailed magnetic studies on (multi-)heme proteins from ammonia oxidizing bacteria. In these systems, both the 24 heme hydroxylamine-oxidoreductase (HAO) and tetra-heme cytochrome c554 revealed a novel type of weak heme-heme interaction where the EPR resonances were found frequency dependent. This was determined by the use of parallel mode EPR for integer spin EPR in combination with Mössbauer spectroscopy. The ferric cytochrome c554 has a very unusual low temperature EPR spectrum at neutral pH with a very broad resonance and zero crossing at g = 3.3 at (X-band EPR 9.2 GHz). The whole spectrum is shifted in S-band EPR (3.3 GHz) with the zero crossing at at g = 3.0. The novel P460 chromophore in HAO and the P460-cytochrome both in their reduced forms has an unusually large quadrupole doublet (Eq = 4.2 mm/sec seen by Mössbauer spectroscopy). The ferric P460 has an integer spin EPR signal in HAO due to spin coupling to one other heme. Also for this state the EPR spectra changed with EPR frequency (published in J. Am. Chem. Soc., J. Biol. Chem.). These novel findings of weak magnetic couplings and novel heme groups have later been found in other proteins. Other Mössbauer studies include examination of di-iron oxygen proteins such as the hydroxylase components of soluble methane monooxygenase (with E. Münck, published in J. Am. Chem. Soc.) and of the RiboNucleotide Reductase (RNR) p53R2 protein (unpublished with Åsmund K. Røhr, V. Schünemann and A.X. Trautwein) in different redox states. These clusters, Cu-proteins and radicals were further examined with e.g. protein crystallography, Raman, magnetic circular dichroism (with Edward I. Solomon, Stanford University) and EPR up to 285 GHz (with Anne-Laure Barra, CNRS Grenoble). Recently we the Andersson Group studied mono-heme cytochrome c552 from ammonia oxidizing bacteria with Mössbauer spectroscopy (with Volker Schünemann and Alfred X. Trautwein in Germany) in combination with EPR and paramagnetic NMR (with Kara L. Bren). We could find a novel correlation between the unusual highly anisotropic low spin (HALS) ferric cytochrome c552 EPR signals with large gmax values and their paramagnetic shifted heme methyl groups (published in J. Am. Chem. Soc.). Furthermore we have examined with Mössbauer, EPR, Raman and single protein crystal light absorption spectroscopy a Fe(IV)OH form of hydrogenperoxide oxidized myoglobin compound II (published in J. Biol. Chem). We are together with Volker Schünemann preparing experiments using the recently developed 57Fe dependent technique Nuclear Resonance Scattering and Raman Microscopy in order to further characterize the myoglobin compound II as well as our novel peroxy-myoglobin.

• Seibel, HA; Karen, Pavel; Wagner, TR & Woodward, PM (2009). Synthesis and characterization of color variants of nitrogen- and fluorine-substituted TiO2. Journal of Materials Chemistry. ISSN 0959-9428. 19(4), p. 471–477. doi: 10.1039/b815758h.
• Woodward, PM; Goldberger, J; Stoltzfus, MW; Eng, HW; Ricciardo, RA & Santhosh, PN [Show all 8 contributors for this article] (2008). Electronic, magnetic, and structural properties of Sr2MnRuO6 and LaSrMnRuO6 double perovskites. Journal of The American Ceramic Society. ISSN 0002-7820. 91, p. 1796–1806. doi: 10.1111/j.1551-2916.2008.02412.x.
• Karen, Pavel; Gustafsson, K & Linden, J (2007). EuBaFe2O5: Extent of charge ordering by Mossbauer spectroscopy and high-intensity high-resolution powder diffraction. Journal of Solid State Chemistry. ISSN 0022-4596. 180. doi: 10.1016/j.jssc.2006.09.021.
• Chang, S; Karen, Pavel; Hehlen, MP; Trouw, FR & McQueeney, RJ (2007). Damping of antiferromagnetic spin waves by valence fluctuations in the double layer perovskite YBaFe2O5. Physical Review Letters. ISSN 0031-9007. 99. doi: 10.1103/PhysRevLett.99.037202.
• Karen, Pavel; Gustafsson, K & Linden, J (2007). EuBaFe2O5+w: Valence mixing and charge ordering are two separate cooperative phenomena. Journal of Solid State Chemistry. ISSN 0022-4596. 180, p. 148–157. doi: 10.1016/j.jssc.2006.09.031.
• Karen, Pavel (2006). Nonstoichiometry in oxides and its control. Journal of Solid State Chemistry. ISSN 0022-4596. 179, p. 3167–3183. doi: 10.1016/j.jssc.2006.06.012.
• Karen, Pavel; Moodenbaugh, AR; Goldberger, J; Santhosh, PN & Woodward, PM (2006). Electronic, magnetic and structural properties of A(2)VMoO(6) perovskites (A = Ca, Sr). Journal of Solid State Chemistry. ISSN 0022-4596. 179. doi: 10.1016/j.jssc.2006.04.013.
• Linden, J; Karen, Pavel; Nakamura, J; Karppinen, M & Yamauchi, H (2006). Transport and magnetotransport properties across the two-step Verwey transition in BaGdFe2O5+w. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 73. doi: 10.1103/PhysRevB.73.064415. Full text in Research Archive
• Karen, Pavel; Suard, Emmanuelle & Fauth, Francois (2005). Crystal Structure of Stoichiometric YBa2Fe3O8. Inorganic Chemistry. ISSN 0020-1669. 44, p. 8170–8172. doi: 10.1021/ic048746b.
• Karen, Pavel (2004). Chemistry and thermodynamics of the twin charge-ordering transitions in RBaFe2O5+w series. Journal of Solid State Chemistry. ISSN 0022-4596. 177, p. 281–292. doi: 10.1016/j.jssc.2003.08.011.
• Lindén, Johan; Karen, Pavel; Yamauchi, Hisao & Karppinen, Maarit (2004). Valence mixing, separation and ordering in double-cell perovskite GdBaFe2O5+w. Journal of Magnetism and Magnetic Materials. ISSN 0304-8853. 272-276, p. E267–E268. doi: 10.1016/j.jmmm.2003.11.181.
• Lindén, Johan; Karen, Pavel; Yamauchi, Hisao & Karppinen, Maarit (2004). Exploring the Verwey-Type Transition in GdBaFe2O5+w Using 57Fe Moessbauer Spectroscopy. Hyperfine Interactions. ISSN 0304-3843. 156/157(1-4), p. 321–325. doi: 10.1023/B%3AHYPE.0000043248.99004.65.
• Karen, Pavel; Suard, Emmanuelle; Fauth, Francois & Woodward, Patrick M. (2004). YBaMnCoO5; neither valence mixed nor charge ordered. Solid State Sciences. ISSN 1293-2558. 6(11), p. 1195–1204. doi: 10.1016/j.solidstatesciences.2004.06.010.
• Moritomo, Y; Hanawa, M; Xu, S; Ishikawa, H; Ohishi, Y & Kato, K [Show all 10 contributors for this article] (2004). Pressure effects on the charge-ordering transition of BaYCo2O5.0. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 69, p. art. no.–134118. doi: 10.1103/PhysRevB.69.134118. Full text in Research Archive
• Nakamura, J; Karppinen, M; Karen, Pavel; Linden, J & Yamauchi, H (2004). Isovalent-substitution effect on the Verwey-type transition in the A-site-ordered double perovskite (Ba,Sr)RFe2O5. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 70. doi: 10.1103/PhysRevB.70.144104. Full text in Research Archive
• Karen, Pavel; Kjekshus, Arne; Huang, Q.; Karen, V. L.; Lynn, J. W. & Rosov, N. [Show all 8 contributors for this article] (2003). Neutron powder diffraction study of nuclear and magnetic structures of oxidized and reduced YBa2Fe3O8+w. Journal of Solid State Chemistry. ISSN 0022-4596. 174, p. 87–95. doi: 10.1016/S0022-4596%2803%2900180-4.
• Huang, Q. Z.; Karen, V. L.; Santoro, A.; Kjekshus, Arne; Lindén, Johan & Pietari, T. [Show all 7 contributors for this article] (2003). Substitution of Co3+ in YBa2Fe3O8. Journal of Solid State Chemistry. ISSN 0022-4596. 172, p. 73–80. doi: 10.1016/S0022-4596%2802%2900122-6.
• Woodward, Patrick M. & Karen, Pavel (2003). Mixed valence in YBaFe2O5. Inorganic Chemistry. ISSN 0020-1669. 42(4), p. 1121–1129. doi: 10.1021/ic026022z.
• Woodward, Patrick M.; Suard, Emmanuelle & Karen, Pavel (2003). Structural tuning of charge, orbital, and spin ordering in double-cell perovskite series between NdBaFe2O5 and HoBaFe2O5. Journal of the American Chemical Society. ISSN 0002-7863. 125, p. 8889–8899. doi: 10.1021/ja034813.
• Karen, Pavel (2003). Effects of oxygen nonstoichiometry and of its distribution on Verwey-type transitions and structure of GdBaFe2O5+w. Journal of Solid State Chemistry. ISSN 0022-4596. 170, p. 9–23. doi: 10.1016/S0022-4596%2802%2900008-7.
• Karen, Pavel; Woodward, Patrick M.; Santhosh, P.N.; Vogt, Tom; Stephens, P.W. & Pagola, S. (2002). Verwey transition under oxygen loading in RBaFe2O5+w (R = Nd and Sm). Journal of Solid State Chemistry. ISSN 0022-4596. 167, p. 480–493. doi: 10.1006/jssc.2002.9665. Show summary

  Double-cell perovskites RBaFe2O5+w, (R = Nd and Sm) are synthesized in the -0.03 < w < 0.47 portion of the nonstoichiometry range. The ideal composition with w = 0 has di- and trivalent iron in equal proportions and exhibits a charge-ordering Verwey transition upon cooling, preceded by a weaker premonitory transition. Both transitions are detectable by differential scanning calorimetry. The changes in entropy, volume, orthorhombic distortion and electrical conductivity at the main transition are larger for the variant with the smaller Sm atom than for R = Nd. The discontinuity of the SmBaFe2O5+w,, transition also persists into much higher levels of the oxygen nonstoichiometry w than for the R = Nd variant. Whereas 3D-charge-ordered SmBaFe2O5.00 is isostructural with TbBaFe2O5.00 adopting space group Pmma, NdBaFe2O5.00 undergoes a more profound structural change upon entering the charge-ordered state, the structure of which is refined in the P21ma symmetry from high-resolution X-ray synchrotron diffraction data.

• Karen, Pavel; Woodward, Patrick M.; Lindén, Johan; Vogt, Tom; Studer, Andrew & Fischer, Peter (2001). Verwey transition in mixed-valence TbBaFe2O5: Two attempts to order charges. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 64(21), p. 214405/1–/14. doi: 10.1103/PhysRevB.64.214405. Full text in Research Archive
• Karen, Pavel; Kjekshus, Arne; Huang, Q.; Karen, V. L.; Mighell, A. D. & Santoro, A. (2000). Neutron powder diffraction study of the crystal structure of the oxycarbonate phase YBa2Cu2.85(CO3)0.15O6.73. Physica. C, Superconductivity. ISSN 0921-4534. 336, p. 279–286. doi: 10.1016/S0921-4534%2800%2900275-6.
• Vogt, Tom; Woodward, Patrick M.; Karen, Pavel; Hunter, B.A.; Henning, P. & Moodenbaugh, A.R. (2000). Low to High Spin-State Transition Induced by Charge Ordering in Antiferrimagnetic YBaCo2O5. Physical Review Letters. ISSN 0031-9007. 84(13), p. 2969–2972. doi: 10.1103/PhysRevLett.84.2969. Full text in Research Archive
• Karen, Pavel; Kjekshus, Arne; Huang, Q. & Karen, V. L. (1999). The Crystal Structure of Magnesium Dicarbide. Journal of Alloys and Compounds. ISSN 0925-8388. 282, p. 72–75. doi: 10.1016/S0925-8388%2898%2900828-7. Show summary

  The crystal structure of MgC<SUB>2</SUB> is solved from powder X-ray and neutron diffraction data. Magnesium dicarbide is synthesized from Mg powder and ethyne, with yields up to 40wt.% (balance: unreacted Mg and MgO). The X-ray pattern is indexed on a tetragonal unit cell, with space group P4<SUB>2</SUB>/mnm suggested from systematic extinctions. The unit cell refined from the powder neutron data has a=3.9342(7) and c=5.021(1)Å and Z=2. The crystal structure contains C<SUB>2</SUB> groups, with a triple-bond length of 1.215(6)Å, aligned into ... MgCCMgCCMg... chains having Mg-C bond lengths of 2.174(4)Å and a weak interaction [2.510(1)Å] between Mg and the triple bond of the crossing chains above and below.

• Karen, Pavel & Woodward, Patrick M. (1999). Synthesis and Structural Investigations of the Double Perovskites REBaFe<SUB>2</SUB>O<SUB>5+w</SUB> (RE = Nd, Sm). Journal of Materials Chemistry. ISSN 0959-9428. 9, p. 789–797. doi: 10.1039/A809302D.
• Lindén, Johan; Karen, Pavel; Kjekshus, Arne; Miettinen, J.; Pietari, T. & Karppinen, Maarit (1999). Valence State Mixing and Separation in SmBaFe2O5+w. Physical Review B. Condensed Matter and Materials Physics. ISSN 1098-0121. 60(22), p. 15251–15260. doi: 10.1103/PhysRevB.60.15251. Full text in Research Archive
• Lindén, Johan; Karen, Pavel; Kjekshus, Arne; Miettinen, J. & Karppinen, Maarit (1999). Partial Oxygen Ordering in Cubic Perovskite REBa2Fe3O8+w (RE= Gd, Eu, Sm, Nd). Journal of Solid State Chemistry. ISSN 0022-4596. 144, p. 398–404. doi: 10.1006/jssc.1999.8178.
• Karen, Pavel & Norby, Truls Eivind (1998). La1−xBaxCr1−yTiyO3 with varied oxygen content. Journal of the Electrochemical Society. ISSN 0013-4651. 145, p. 264–269. doi: 10.1149/1.1838245.
• Karen, Pavel; Kjekshus, Arne; Huang, Q; Lynn, J.W.; Rosov, N. & Natali-Sora, I. [Show all 9 contributors for this article] (1998). Neutron and X-ray powder diffraction study of REBa2Fe3O8+w phases. Journal of Solid State Chemistry. ISSN 0022-4596. 136, p. 21–33. doi: 10.1006/jssc.1997.7636.
• Lindén, Johan; Lippmaa, Mikk; Kjekshus, Arne; Karen, Pavel & Karppinen, Maarit (1998). A 57Fe Mössbauer study of the cubic perovskite-type phase LaBa2Fe3O8+w (−0.20 < w < 0.83). Journal of Solid State Chemistry. ISSN 0022-4596. p. 87–97. doi: 10.1006/jssc.1998.7757.
• Karen, Pavel; Harlow, R.L.; Li, Z.; Meenan, P & Parziale, P.A. (1998). The crystal structure of 2-amino-4,6-dihydroxypyrimidine determined from powder X-ray synchrotron diffraction. Acta Chemica Scandinavica. ISSN 0904-213X. 52, p. 1051–1055. doi: 10.3891/acta.chem.scand.52-1051.
• Linden, Johan; Kjekshus, Arne; Karen, Pavel; Miettinen, J. & Karppinen, Maarit (1998). A 57Fe Mössbauer study of REBa2Fe3O8+w triple perovskites with varied oxygen content (RE = Dy, Er and Y). Journal of Solid State Chemistry. ISSN 0022-4596. 139, p. 168–175. doi: 10.1006/jssc.1998.7828.
• Karen, Pavel & Woodward, Patrick M. (1998). Liquid-mix disorder in crystalline solids; ScMnO3. Journal of Solid State Chemistry. ISSN 0022-4596. 141, p. 78–88. doi: 10.1006/jssc.1998.7918.
• Woodward, Patrick M.; Vogt, Tom; Cox, D. E.; Arulraj, A.; Rao, C.N.R. & Karen, Pavel [Show all 7 contributors for this article] (1998). The infuence of cation size on the structural features of Ln1/2A1/2MnO3 perovskites at room temperature. Chemistry of Materials. ISSN 0897-4756. 10, p. 3652–3665. doi: 10.1021/cm980397u.
• Karen, Pavel & Kjekshus, Arne (1997). Chemical phase diagrams in the YBa2Cu3O7 family, ANNO 1996. Journal of Thermal Analysis and Calorimetry. ISSN 1388-6150. 48, p. 1143–1227. doi: 10.1007/BF01979159.
• Natali-Sora, I.; Huang, Q.; Lynn, J.W.; Rosov, N.; Karen, Pavel & Kjekshus, Arne [Show all 9 contributors for this article] (1994). Neutron-powder-diffraction study of the nuclear and magnetic structures of the substitution compound (Y1−xCax)Ba2Fe3O8+d (x = 0.05, 0.10 and 0.20). Physical review B (PRB). ISSN 2469-9950. 49, p. 3465–3472. doi: 10.1103/PhysRevB.49.3465. Full text in Research Archive
• Huang, Q; Karen, Pavel; Karen, V.L.; Kjekshus, Arne; Lynn, J.W. & Mighell, A.D. [Show all 9 contributors for this article] (1994). Neutron-powder-diffraction study of the nuclear and magnetic structures of the oxygen-defficient perovskite YBaCuCoO5. Journal of Solid State Chemistry. ISSN 0022-4596. 108, p. 80–86. doi: 10.1006/jssc.1994.1012.
• Fjellvåg, Helmer & Karen, Pavel (1994). Crystal structure of ScCl3. Acta Chemica Scandinavica. ISSN 0904-213X. 48, p. 294–297. doi: 10.3891/acta.chem.scand.48-0294. Full text in Research Archive
• Karen, Pavel & Kjekshus, Arne (1994). Citrate-gel syntheses in the Y(O)—Ba(O)—Cu(O) system. Journal of The American Ceramic Society. ISSN 0002-7820. 77, p. 547–552. doi: 10.1111/j.1151-2916.1994.tb07028.x.
• Atanassova, Y.K.; Hadijev, V.G.; Karen, Pavel & Kjekshus, Arne (1994). Raman scattering from YBa2Fe3O8+d. Physical review B (PRB). ISSN 2469-9950. 50, p. 586–589. doi: 10.1103/PhysRevB.50.586. Full text in Research Archive
• Karen, Pavel & Kjekshus, Arne (1994). YBa2Fe3O8 with varied oxygen content. Journal of Solid State Chemistry. ISSN 0022-4596. 112, p. 73–77. doi: 10.1006/jssc.1994.1267.
• Karen, Pavel & Kjekshus, Arne (1993). Magnetic properties of YBaCuCoO5. Acta Chemica Scandinavica. ISSN 0904-213X. 47, p. 1041–1042. doi: 10.3891/acta.chem.scand.47-1041. Full text in Research Archive
• Karen, Pavel; Braaten, O. & Kjekshus, Arne (1992). Chemical phase diagrams for the YBa2Cu3O7 family. Acta Chemica Scandinavica. ISSN 0904-213X. 46, p. 805–840. doi: 10.3891/acta.chem.scand.46-0805. Full text in Research Archive
• Karen, Pavel & Fjellvåg, Helmer (1992). Hydrolysis and structure of carbides related to propadiene. Journal of Alloys and Compounds. ISSN 0925-8388. 178, p. 289–295. doi: 10.1016/0925-8388%2892%2990270-J.
• Karen, Pavel; Kjekshus, Arne & Andresen, A.F. (1992). Superconducting and structural properties of Sr-substituted YBa2Cu4O8. Acta Chemica Scandinavica. ISSN 0904-213X. 46, p. 1059–1064. doi: 10.3891/acta.chem.scand.46-1059. Full text in Research Archive
• Karen, Pavel; Fjellvåg, Helmer & Kjekshus, Arne (1992). Superconductivity in Y(Ba1−yLay)2Cu3O9−d. Journal of Solid State Chemistry. ISSN 0022-4596. 97, p. 257–273. doi: 10.1016/0022-4596%2892%2990033-R.
• Karen, Pavel; Andresen, P.H. & Kjekshus, Arne (1992). YBa2Fe3O8 and the YCu(O)—BaCu(O)—YFe(O)—BaFe(O) phase diagram. Journal of Solid State Chemistry. ISSN 0022-4596. 101, p. 48–58. doi: 10.1016/0022-4596%2892%2990199-6.
• Fjellvåg, Helmer & Karen, Pavel (1992). The crystal structure of magnesium sesquicarbide. Inorganic Chemistry. ISSN 0020-1669. 31, p. 3260–3263. doi: 10.1021/ic00041a018.
• Huang, Q.; Karen, Pavel; Karen, V.L.; Kjekshus, Arne; Lynn, J.W. & Mighell, A.D. [Show all 8 contributors for this article] (1992). Neutron-powder-diffraction study of the nuclear and magnetic structures of YBa2Fe3O8 at room temperature. Physical review B (PRB). ISSN 2469-9950. 45, p. 9611–9619. doi: 10.1103/PhysRevB.45.9611. Full text in Research Archive
• Karen, Pavel; Fjellvåg, Helmer; Kjekshus, Arne & Andresen, A.F. (1991). On phase relations, structural and magnetic properties of the stable manganese carbides Mn23C6, Mn5C2 and Mn7C3. Acta Chemica Scandinavica. ISSN 0904-213X. 45, p. 549–557. doi: 10.3891/acta.chem.scand.45-0549. Full text in Research Archive
• Andresen, P.H.; Fjellvåg, Helmer; Karen, Pavel & Kjekshus, Arne (1991). Substitution for copper in YBa2Cu3O9−d by 3d- and pre-transition metals. Acta Chemica Scandinavica. ISSN 0904-213X. 45, p. 698–708. doi: 10.3891/acta.chem.scand.45-0698. Full text in Research Archive
• Karen, Pavel; Fjellvåg, Helmer; Kjekshus, Arne & Andresen, A.F. (1991). Chemical pressure and other effects of strontium substitution in YBa2Cu3O9−d. Journal of Solid State Chemistry. ISSN 0022-4596. 92, p. 57–67. doi: 10.1016/0022-4596%2891%2990242-A.
• Karen, Pavel; Fjellvåg, Helmer; Kjekshus, Arne & Andresen, A.F. (1991). Lanthanum substitution for barium in YBa2Cu3O9−d. Journal of Solid State Chemistry. ISSN 0022-4596. 93, p. 163–172. doi: 10.1016/0022-4596%2891%2990285-P.
• Karen, Pavel & Kjekshus, Arne (1991). Oxycarbonates in the Y(O/CO3)—Ba(O/CO3)—Cu(O/CO3) system. Journal of Solid State Chemistry. ISSN 0022-4596. 94, p. 298–305. doi: 10.1016/0022-4596%2891%2990195-N.
• Hasek, J.; Ondracek, J.; Karen, Pavel & Bauer, J. (1990). The crystal and molecular structure of scandium formate. Collection of Czechoslovak Chemical Communications. ISSN 0010-0765. 55, p. 426–434. doi: 10.1135/cccc19900426.
• Fjellvåg, Helmer; Karen, Pavel; Kjekshus, Arne; Zieba, A.; Chattopadhyay, T. & Vettier, C. (1990). Pressure induced transitions between para-, heli-, and ferromagnetic phases of Mn0.61Cr0.39As, studied by neutron diffraction. Journal of Magnetism and Magnetic Materials. ISSN 0304-8853. 92, p. 75–79. doi: 10.1016/0304-8853%2890%2990681-F.
• Karen, Pavel; Fjellvåg, Helmer; Braaten, O.; Kjekshus, Arne & Bratsberg, H. (1990). Lanthanide substitution in YBa2Cu3O9−d. Acta Chemica Scandinavica. ISSN 0904-213X. 44, p. 994–1001. doi: 10.3891/acta.chem.scand.44-0994. Full text in Research Archive
• Fjellvåg, Helmer; Karen, Pavel; Kjekshus, Arne & Andresen, A.F. (1989). Superconducting properties in relation to chemical pressure in YBa2Cu3O9−d. Physica. C, Superconductivity. ISSN 0921-4534. 162-164. doi: 10.1016/0921-4534%2889%2990911-8.
• Fjellvåg, Helmer; Karen, Pavel; Kjekshus, Arne; Lyng, S. & Braaten, O. (1988). Is mutual separation of rare earth elements crucial for high-Tc materials? Physica. C, Superconductivity. ISSN 0921-4534. 153-155, p. 1421–1422. doi: 10.1016/0921-4534%2888%2990351-6.

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• Woodward, Patrick M.; Karen, Pavel; Evans, John S. O. & Vogt, Thomas (2021). Solid State Materials Chemistry. Cambridge University Press. ISBN 9780521873253. 708 p.
• Karen, Pavel & Furuseth, Sigrid Breien (2004). KJM1010 Kjemiske strukturer og prinsipper - Tilleggskompendium: Konsepter i uorganisk reaksjonskjemi. Universitetet i Oslo, Reprosentralen. 24 p.
• Karen, Pavel & Benneche, Tore (2004). KJM1010 Kjemiske strukturer og prinsipper - Laboratoriekurs. Universitetet i Oslo, Reprosentralen. 81 p.

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• Karen, Pavel (2008). Most pressurized elements aren't simple cubic. Physics today. ISSN 0031-9228. 61, p. 10–10.
• Karen, Pavel (2008). Valence mixing and ordering in RBaFe2O5+w.
• Karen, Pavel (2007). Valence-mixed compounds (Fe3O4 and RBaFe2O5).
• Karen, Pavel (2005). What is Verwey transition and why it may matter.
• Karen, Pavel (2005). Nonstoichiometry in oxides and its control.
• Karen, Pavel (2005). Verwey transition in a perovskite-type structure. Show summary

  Above Verwey transition at 120 K, magnetite (Fe3O4) is a spin-polarized conductor, feasible for applications in spin computing. Owing to continuing controversy about charge order in the complex low-temperature phase, Verwey transition in magnetite remains a mystery. Double-cell perovskites of the YBaFe2O5 type contain iron in the average oxidation state +2.5 and exhibit all symptoms of the Verwey transition. The charge-ordered superstructures are simple and the refined iron–oxygen bond distances suggest a 70 to 80% of long-range charge separation into di- and trivalent iron, likely to mean a 100% charge separation on the local scale. The charge order violates Coulombic minimization of point charges, implying orbital ordering. The associated orthorhombic distortion identifies the doubly-occupied dxz orbital of Fe2+. Magnetic interactions define the orientation of the orthorhombic distortion, but the charge order occurs independently of any specific spin coupling. Magnetostriction opens for an incipient partial charge ordering that occurs before the Verwey transition itself distorts the structure under continued cooling. Replacing Y with Sm and Nd shows that when the size of this seemingly uninvolved atom becomes unfavorable (a large projected ∆V at the transition), orbital ordering continues at a cost of symmetry lowering. Oxygen nonstoichiometry decreases Verwey-transition entropies ΔS and transition temperatures TV in a manner that corresponds to an ideal solution of YBaFe2O6 in the YBaFe2O5 solvent. Verwey transition is a klassengleich switch from a valence-mixed halfmetal into a valence-ordered semiconductor, achieved via orbital ordering of one single, singly or doubly occupied d orbital of t2g symmetry.

• Karen, Pavel (2004). What RBaFe2O5+w tells us about Verwey transition and why it matters.
• Karen, Pavel (2002). Charge ordering that only succeeds after nature's second attempt.
• Karen, Pavel; Woodward, Patrick M. & Lindén, Johan (2002). Charge ordering that only succeeds after nature's second attempt.
• Karen, Pavel & Kjekshus, Arne (2000). Phase Diagrams and Thermodynamic Properties. In Gschneidner, Karl A. Jr.; Eyring, LeRoy & Maple, Brian M. (Ed.), Handbook on the Physics and Chemistry of the Rare Earths. Volume 30, High-Temperature Superconductors - I. Elsevier Science B.V., The Netherlands. ISSN 0-444-50528-8. p. 229–373. doi: 10.1016/S0168-1273%2800%2930007-1.
• Lindén, Johan; Nakamura, Jin; Karen, Pavel; Kjekshus, Arne; Karppinen, Maarit & Yamauchi, Hisao (2000). Observation of mixed-valence state in the BaSm(Cu1-xFex)2O5+.delta.double-perovskite phase.
• Karen, Pavel (1999). Ordering, Mixed-Valence and Metallic Character Along the Redox Range in LnBaM2O5+w (M = Fe and Co). Show summary

  A full replacement of the perovskite coordination-octahedra With ordered square pyramids leads to doubling of the unit-cell according to formula AA'M2O5. Suitably sized trivalent lanthanides (Ln) as A atoms and Ba as the A' atom are able to stabilize this arrangement for transition metals M like Mn, Fe and Co. The implied non-integer average valence M2.5+ and an entire vacant oxygen site are the main ingredients for a multitude of structural, electronic, magnetic and electric properties changing along a wide solid-state redox-stability range. LnBaM2O5+w phases with selected combinations of Ln = Nd, Sm, Gd, Y and M = Fe, Co are studied on quenched samples with w varied between 0.00 and 0.80. Structural consequences are investigated by powder neutron and synchrotron X-ray diffraction and involve distortions of the tetragonal (S.G. P4/mmm) prototype and/or further ordering schemes for significant compositions in terms of w. Valence and spin states of M are studied by 57Fe Mössbauer spectroscopy (for M = Co, 1% of it is replaced by 57Fe). A mixed-valence AF state Fe2.5+ is observed at room temperature for the prototype composition and fades away with increasing w. Upon cooling below the transition temperature of around 200 K, the Fe2.5+ state separates into a high-spin Fe3+ state and Fe2+ with unusually low internal magnetic field. The transition is associated with a small change in magnetic susceptibility and a weak thermal effect, implying a charge ordering into an electron localized state. Samples with the most reduced M = Fe and the most oxidized M = Co have a silver luster appearance at room temperature, and optical reflectivity spectra as well as electrical conductivity measurements illustrate changes in the occurrence of the metallic character as a function of w and temperature. The Fe2.5+ valence state mixing coincides with the metallic state and is therefore closely reminiscent of the Verwey transition in magnetite, Fe3O4, one of the earliest examples of charge ordering in a transition metal oxide.

• Karen, Pavel (2017). KJM1120 Uorganisk kjemi, Laboratoriekurs høstsemester 2017. Reprosentralen UiO.
• Karen, Pavel (2017). KJM 1120 Uorganisk kjemi, Laboratoriekurs høstsemester 2017. Reprosentralen UiO.
• Karen, Pavel (2008). KJM1120 Uorganisk kjemi, Laboratoriekurs, høstsemester 2008. Reprosentralen UiO.
• Karen, Pavel (2007). KJM1030 Uorganisk kjemi Laboratoriekurs, vårsemester 2007. Reprosentralen UiO.
• Karen, Pavel (2006). KJM1030 Uorganisk kjemi, Laboratoriekurs, vårsemester 2006. Reprosentralen.
• Karen, Pavel (2006). KJM1021 Kjemisk Struktur og Reaktivitet, Laboratoriekurs uorganisk del høstsemesteret 2006. UiO Reprosentralen.
• Karen, Pavel (2005). KJM1030 Uorganisk kjemi, Laboratoriekurs, vårsemester 2005. Reprosentralen UiO.
• Karen, Pavel & Benneche, Tore (2005). KJM1010 Kjemiske strukturer og prinsipper, Laboratoriekurs, vårsemester 2005. Reprosentralen UiO.
• Karen, Pavel (2004). Tuning the Verwey transition as an orbital ordering, ILL Annual Report 2003, p.24-5. Institute Laue--Langevin.
• Karen, Pavel (2002). KJ 102 Uorganisk kjemi, Laboratoriekurs, høstsemester 2002. Kjemisk institutt.
• Karen, Pavel (2001). KJ110 Uorganisk kjemi I; Laboratoriekurs, høstsemester 2001. Kjemisk institutt, Universitetet i Oslo.
• Karen, Pavel (2000). KJ 110 Uorganisk kjemi I; Laboratoriekurs, høstsemester 2000. Kjemisk institutt, Universitetet i Oslo.

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