György Lovas | Eötvös Loránd University (original) (raw)

Papers by György Lovas

Acta Mineralogica-Petrographica, 2004

In this paper, a new laboratory procedure is presented for the separation of micas from quartz in... more In this paper, a new laboratory procedure is presented for the separation of micas from quartz in clay-sized materials. The key part of the procedure consists of centrifuging the clay-sized material in a non-reactive, high-viscosity medium (2% solution of sodium carboxymethyl cellulose). As a result of the centrifugation, platy clay minerals stay in suspension while quartz grains settle down. After centrifugation, the water-soluble carboxymethyl cellulose can be easily washed out of the clay mineral separate. The ...

Original szaibelyite Mg2(0H)[B20.)(0H)] material from its type-locality (Rézbánya, Bihar Mts., Ru... more Original szaibelyite Mg2(0H)[B20.)(0H)] material from its type-locality (Rézbánya, Bihar Mts., Rumania) has been investigated. Starting with an XPD ab initio determination, its unit cell was refined to the values of a=12.571(l), 6=10.4025(9), c=3.1333(4) Á and p=95°54.2(9)' in P2,/a symmetry. The crystal structure was refined by Rietveld method on the basis of TAKÉUCHI'S (1973) model. The results converged to an atomic arrangement similar to the one determined for a szaibelyite sample from Königshall-Hindenburg, Germany. A search to find traces of an orthorhombic polytype in the XPD pattern, due to the 2| pseudosymmetry, failed to identify any. Neither was successful the attempt to find significant differences between the szaibelyite and a sample called 'ascharite' from Stassfiirt. TEM investigations revealed, that the [001] elongated crystallites of szaibelyite occur in bundles in which the individual fibres are randomly oriented around their c axis. Its most characteristic real structural feature is the (100) twinning producing weak diffuse scattering parallel to the a* axis in the SAED patterns. No polytype modifications or periodic twinning of the basic crystal structure were observed in the material. These results confirm the priority of the original description of szaibelyite (PETERS, 1861). In spite of the low accuracy of the early chemical analysis, the original description proved to be valid and in good accordance with the recent results.

K-feldspars were examined by X-ray powder diffraction method to establish their structural state ... more K-feldspars were examined by X-ray powder diffraction method to establish their structural state in order to assess their condition of formation. [110] and [1-10] translation, calculated from unit cell parameters and unit cell volume obtained by Rietveld refinement gave Al content in t1o site in the range of 0.60 and 0.63 and higher than 0.84 for granitoid rock type and higher than 0.91 for pegmatite and migmatite rock type.

Journal of Thermal Analysis and Calorimetry, 2005

Summary The interaction of cypermethrin with β-cyclodextrin was investigated using different (cop... more Summary The interaction of cypermethrin with β-cyclodextrin was investigated using different (coprecipitation, suspension, kneading and ‘melting in solution’) complexation methods and qualifying the resulted complexes by UV-spectrophotometry, thermal methods (TG, DTG and DSC) and X-ray powder diffraction. The total guest content of complexes can be measured by UV-spectrophotometry in aqueous ethanol solution, while the uncomplexed guest fraction of samples can

Journal of Solid State Chemistry, 1998

The polymorphic phase transitions of Bi 2 Te 4 O 11 have been investigated using X-ray powder dif... more The polymorphic phase transitions of Bi 2 Te 4 O 11 have been investigated using X-ray powder diffraction (XPD), selected area electron diffraction (SAED), and differential scanning calorimetry (DSC) in the 25-730°C range. The metastable cubic modification, which forms under fast crystalization of the Bi 2 Te 4 O 11 melt, has fluorite-type structure. Each cation position is filled with bismuth and tellurium in 1/3-2/3 ratio, while the anion positions are occupied by oxygen in 11/12 site occupancy (evenly distributed vacancy), representing a structure with no chemical ordering. The first process in the transition of cubic phase is cation ordering along a cubic [1 1 1] direction. The ordering process has a small activation energy, but the structure reordering itself is exotherm. The final stage of this ordering is the separation of the cations into the triplets of planes forming two types of structural slabs with composition Bi 2 Te 2 O 7 and TeO 2. Every third plane contains only Te, and the first two are occupied by equal amounts, of Bi and Te with random distribution. The oxygen content is lower than what would be expected based on the available anion sites in the ideal fluorite structure, and these positions are populated by oxygen in a statistical (random) distribution. The next step of transition is the ordering of oxygen vacancy. The oxygen vacancy is concentrated at the Bi-containing layers in accordance with the fluorite-based structural model of the Bi 2 Te 2 O 7 layers. The result is monoclinic Bi 2 Te 4 O 11 with P2 1 /n symmetry. There are, however, several grains in the sample that show the coexistence of an exclusively cation-ordered, fluorite-type structure and that of Rossel's model. This indicates an intermediate or alternative stage of the phase transition, in which the Bi 2 Te 2 O 7 and TeO 2 slabs are already formed, but the oxygen coordination in the TeO 2 layer is still fluorite-type hexahedral. The formation of the rutile-type TeO 2 slabs can be a next step of the transition. The boundary between the two observed phases is irregular. The solid state first order phase transformation can be assumed at the grain boundaries.

Journal of Solid State Chemistry, 1996

For single-crystal growth of bismuth tellurites it is im-The solid state reaction in a 1 : 4 mole... more For single-crystal growth of bismuth tellurites it is im-The solid state reaction in a 1 : 4 mole ratio mixture of Bi 2 O 3 portant to know the details of the solid state reaction beand TeO 2 and the polymorphic phase transition of Bi 2 Te 4 O 11 tween Bi 2 O 3 and TeO 2. There are some contradictions in have been investigated using differential scanning calorimetry the published phase diagrams of this reaction (12, 13). In (DSC), electron microprobe, X-ray powder diffraction (XPD), spite of the fact that bismuth tellurites can easily be oxiand selected area electron diffraction (SAED) analysis in the dized in air there are still some open questions concerning 25-730؇C temperature range. Upon heating first a 8Bi 2 Te 4 O 11 ؉ the oxidation process (12-14). Bismuth tellurium oxide 23TeO 2 eutectic is formed, which melts at 598.9؇C. In this melt compounds have anion-deficient fluorite structures. It is the excess of Bi 2 O 3 reacts further and the Bi 2 O 3 ؉ 4TeO 2 ‫؍‬ not yet clear whether complete oxidation leading to the Bi 2 Te 4 O 11 reaction takes place. The cubic modification is formed filling of all vacant oxygen sites is possible. by fast crystallization of the Bi 2 Te 4 O 11 melt. The structure of The chemical reaction between Bi 2 O 3 and TeO 2 can be the cubic Bi 2 Te 4 O 11 can be characterized by the lattice constant described by the following equation: of a ‫؍‬ 5.6397(5) Å and space group Fm3m. The main product of a slow cooling is the same cubic polymorph although a subordinate formation of the monoclinic phase is also observed. (1 Ϫ x)/2Bi 2 O 3 ϩ xTeO 2 ϭ Bi 1Ϫx Te x O (3ϩx)/2. The ␤-Bi 2 Te 4 O 11 cubic phase undergoes a monotropic transformation into the ␣-Bi 2 Te 4 O 11 monoclinic modification at temper-Bi 2 Te 4 O 11 (x ϭ 0.667) is the first compound formed in the atures higher than 400؇C. The cubic Ǟ monoclinic transition solid state reaction of Bi 2 O 3 and TeO 2. The structure of is the result of an ordering in one set of ͕111͖ planes and the Bi 2 Te 4 O 11 was first studied by Frit et al. (17) and the comorthogonality of the cubic phase in the [110] projection changes plete structure analysis was carried out by Rossel et al. to monoclinic symmetry. The melting enthalpies of the cubic (18). These authors described only the monoclinic Ͱ-modi-␤-phase and the monoclinic ␣-phase are 35.9 ؎ 3.3 J/g and fication. Demina et al. (15) reported on X-ray investigation 84.3 ؎ 4.3 J/g respectively.

The Analyst, 1999

ABSTRACT

Thestructure-sensitiveandstandardlessphasequantificationmethodbasedon a Rietveldanalysisof X-rayp... more Thestructure-sensitiveandstandardlessphasequantificationmethodbasedon a Rietveldanalysisof X-raypowderdiffractiondatawas comparedtosometraditionaltechniques.It wasfoundthattheRietveld-basedmethodis atleastequal,in severalcasesuperiortotheRIR technique,andcanbeafastandsimplesubstitutefortheopticaimodalanalysis.At thesametimeit is shownthathepointsofaRietveld-basedrockclassification,usingtheQAP rockclassificationof Streckeisen,canbeerroneouslyshiftedonthediagramtowardsthehigher plagioclasecontainingtypesdueto theperthiticexsolutionof K-feldsparandconsequentinherentoverestimationf theabundanceof plagioclase. Keywords:Rietveld,XRD quantification,phaseanalysis,granitoid

The structure-sensitive and standardless phase quantification method based on a Rietveld analysis... more The structure-sensitive and standardless phase quantification method based on a Rietveld analysis of X-ray powder diffraction data was compared to some traditional techniques. It was found that the Rietveld-based method is at least equal, in several cases superior to the RIR technique, and can be a fast and simple substitute for the opticai modal analysis. At the same time it is shown that the points of a Rietveldbased rock classification, using the QAP rock classification of Streckeisen, can be erroneously shifted on the diagram towards the higher plagioclase containing types due to the perthitic exsolution of K-feldspar and consequent inherent overestimation of the abundance of plagioclase.

Journal of Solid State Chemistry

ABSTRACT

Materials Science Forum, 1994

Geologia Croatica, 2011

Potassium feldspars from different granitoids and gneisses of Papuk Mt. (Slavonia, Croatia) have ... more Potassium feldspars from different granitoids and gneisses of Papuk Mt. (Slavonia, Croatia) have been investigated by X-ray powder diffraction. Diffraction patterns classically observed as well as patterns calculated by Rietveld refi nement were compared and discussed. Triclinicity was calculated according to while the structural state of the feldspars was determined using the methods of and GO-DINHO & JALECO (1973). Results showed that the type of potassium feldspar depend on the investigated host-rock, indicating variation in the structural state from orthoclase, intermediate microcline to highly ordered microcline. Potassium feldspar megacrysts in biotite-granodiorites and monzogranites are intermediate microcline or orthoclase, while two-mica monzogranites contain low microcline. Gneisses contain low microcline and orthoclase in Brzaja Creek and low microcline in Djedovica Quarry. Classically observed and digital diffraction patterns calculated by the Rietveld refi nement method produced comparable results and provided a very good correlation of the results obtained by different methods. High triclinicity values of feldspars from investigated granitoid and gneiss samples from Papuk Mt. (Slavonia, Croatia) are in accordance with a high Al content in the T 1 o site and their fully ordered state indicates a slow(er) cooling-rate. Low triclinicity values, an Al content in T 1 o site around 0.60 and ordering index smaller than 0.80 can be interpreted as a result of relatively fast(er) cooling which allowed lower ordering of the potassium feldspar.

Acta Mineralogica-Petrographica, 2004

In this paper, a new laboratory procedure is presented for the separation of micas from quartz in... more In this paper, a new laboratory procedure is presented for the separation of micas from quartz in clay-sized materials. The key part of the procedure consists of centrifuging the clay-sized material in a non-reactive, high-viscosity medium (2% solution of sodium carboxymethyl cellulose). As a result of the centrifugation, platy clay minerals stay in suspension while quartz grains settle down. After centrifugation, the water-soluble carboxymethyl cellulose can be easily washed out of the clay mineral separate. The ...

Original szaibelyite Mg2(0H)[B20.)(0H)] material from its type-locality (Rézbánya, Bihar Mts., Ru... more Original szaibelyite Mg2(0H)[B20.)(0H)] material from its type-locality (Rézbánya, Bihar Mts., Rumania) has been investigated. Starting with an XPD ab initio determination, its unit cell was refined to the values of a=12.571(l), 6=10.4025(9), c=3.1333(4) Á and p=95°54.2(9)' in P2,/a symmetry. The crystal structure was refined by Rietveld method on the basis of TAKÉUCHI'S (1973) model. The results converged to an atomic arrangement similar to the one determined for a szaibelyite sample from Königshall-Hindenburg, Germany. A search to find traces of an orthorhombic polytype in the XPD pattern, due to the 2| pseudosymmetry, failed to identify any. Neither was successful the attempt to find significant differences between the szaibelyite and a sample called 'ascharite' from Stassfiirt. TEM investigations revealed, that the [001] elongated crystallites of szaibelyite occur in bundles in which the individual fibres are randomly oriented around their c axis. Its most characteristic real structural feature is the (100) twinning producing weak diffuse scattering parallel to the a* axis in the SAED patterns. No polytype modifications or periodic twinning of the basic crystal structure were observed in the material. These results confirm the priority of the original description of szaibelyite (PETERS, 1861). In spite of the low accuracy of the early chemical analysis, the original description proved to be valid and in good accordance with the recent results.

K-feldspars were examined by X-ray powder diffraction method to establish their structural state ... more K-feldspars were examined by X-ray powder diffraction method to establish their structural state in order to assess their condition of formation. [110] and [1-10] translation, calculated from unit cell parameters and unit cell volume obtained by Rietveld refinement gave Al content in t1o site in the range of 0.60 and 0.63 and higher than 0.84 for granitoid rock type and higher than 0.91 for pegmatite and migmatite rock type.

Journal of Thermal Analysis and Calorimetry, 2005

Summary The interaction of cypermethrin with β-cyclodextrin was investigated using different (cop... more Summary The interaction of cypermethrin with β-cyclodextrin was investigated using different (coprecipitation, suspension, kneading and ‘melting in solution’) complexation methods and qualifying the resulted complexes by UV-spectrophotometry, thermal methods (TG, DTG and DSC) and X-ray powder diffraction. The total guest content of complexes can be measured by UV-spectrophotometry in aqueous ethanol solution, while the uncomplexed guest fraction of samples can

Journal of Solid State Chemistry, 1998

The polymorphic phase transitions of Bi 2 Te 4 O 11 have been investigated using X-ray powder dif... more The polymorphic phase transitions of Bi 2 Te 4 O 11 have been investigated using X-ray powder diffraction (XPD), selected area electron diffraction (SAED), and differential scanning calorimetry (DSC) in the 25-730°C range. The metastable cubic modification, which forms under fast crystalization of the Bi 2 Te 4 O 11 melt, has fluorite-type structure. Each cation position is filled with bismuth and tellurium in 1/3-2/3 ratio, while the anion positions are occupied by oxygen in 11/12 site occupancy (evenly distributed vacancy), representing a structure with no chemical ordering. The first process in the transition of cubic phase is cation ordering along a cubic [1 1 1] direction. The ordering process has a small activation energy, but the structure reordering itself is exotherm. The final stage of this ordering is the separation of the cations into the triplets of planes forming two types of structural slabs with composition Bi 2 Te 2 O 7 and TeO 2. Every third plane contains only Te, and the first two are occupied by equal amounts, of Bi and Te with random distribution. The oxygen content is lower than what would be expected based on the available anion sites in the ideal fluorite structure, and these positions are populated by oxygen in a statistical (random) distribution. The next step of transition is the ordering of oxygen vacancy. The oxygen vacancy is concentrated at the Bi-containing layers in accordance with the fluorite-based structural model of the Bi 2 Te 2 O 7 layers. The result is monoclinic Bi 2 Te 4 O 11 with P2 1 /n symmetry. There are, however, several grains in the sample that show the coexistence of an exclusively cation-ordered, fluorite-type structure and that of Rossel's model. This indicates an intermediate or alternative stage of the phase transition, in which the Bi 2 Te 2 O 7 and TeO 2 slabs are already formed, but the oxygen coordination in the TeO 2 layer is still fluorite-type hexahedral. The formation of the rutile-type TeO 2 slabs can be a next step of the transition. The boundary between the two observed phases is irregular. The solid state first order phase transformation can be assumed at the grain boundaries.

Journal of Solid State Chemistry, 1996

For single-crystal growth of bismuth tellurites it is im-The solid state reaction in a 1 : 4 mole... more For single-crystal growth of bismuth tellurites it is im-The solid state reaction in a 1 : 4 mole ratio mixture of Bi 2 O 3 portant to know the details of the solid state reaction beand TeO 2 and the polymorphic phase transition of Bi 2 Te 4 O 11 tween Bi 2 O 3 and TeO 2. There are some contradictions in have been investigated using differential scanning calorimetry the published phase diagrams of this reaction (12, 13). In (DSC), electron microprobe, X-ray powder diffraction (XPD), spite of the fact that bismuth tellurites can easily be oxiand selected area electron diffraction (SAED) analysis in the dized in air there are still some open questions concerning 25-730؇C temperature range. Upon heating first a 8Bi 2 Te 4 O 11 ؉ the oxidation process (12-14). Bismuth tellurium oxide 23TeO 2 eutectic is formed, which melts at 598.9؇C. In this melt compounds have anion-deficient fluorite structures. It is the excess of Bi 2 O 3 reacts further and the Bi 2 O 3 ؉ 4TeO 2 ‫؍‬ not yet clear whether complete oxidation leading to the Bi 2 Te 4 O 11 reaction takes place. The cubic modification is formed filling of all vacant oxygen sites is possible. by fast crystallization of the Bi 2 Te 4 O 11 melt. The structure of The chemical reaction between Bi 2 O 3 and TeO 2 can be the cubic Bi 2 Te 4 O 11 can be characterized by the lattice constant described by the following equation: of a ‫؍‬ 5.6397(5) Å and space group Fm3m. The main product of a slow cooling is the same cubic polymorph although a subordinate formation of the monoclinic phase is also observed. (1 Ϫ x)/2Bi 2 O 3 ϩ xTeO 2 ϭ Bi 1Ϫx Te x O (3ϩx)/2. The ␤-Bi 2 Te 4 O 11 cubic phase undergoes a monotropic transformation into the ␣-Bi 2 Te 4 O 11 monoclinic modification at temper-Bi 2 Te 4 O 11 (x ϭ 0.667) is the first compound formed in the atures higher than 400؇C. The cubic Ǟ monoclinic transition solid state reaction of Bi 2 O 3 and TeO 2. The structure of is the result of an ordering in one set of ͕111͖ planes and the Bi 2 Te 4 O 11 was first studied by Frit et al. (17) and the comorthogonality of the cubic phase in the [110] projection changes plete structure analysis was carried out by Rossel et al. to monoclinic symmetry. The melting enthalpies of the cubic (18). These authors described only the monoclinic Ͱ-modi-␤-phase and the monoclinic ␣-phase are 35.9 ؎ 3.3 J/g and fication. Demina et al. (15) reported on X-ray investigation 84.3 ؎ 4.3 J/g respectively.

The Analyst, 1999

ABSTRACT

Thestructure-sensitiveandstandardlessphasequantificationmethodbasedon a Rietveldanalysisof X-rayp... more Thestructure-sensitiveandstandardlessphasequantificationmethodbasedon a Rietveldanalysisof X-raypowderdiffractiondatawas comparedtosometraditionaltechniques.It wasfoundthattheRietveld-basedmethodis atleastequal,in severalcasesuperiortotheRIR technique,andcanbeafastandsimplesubstitutefortheopticaimodalanalysis.At thesametimeit is shownthathepointsofaRietveld-basedrockclassification,usingtheQAP rockclassificationof Streckeisen,canbeerroneouslyshiftedonthediagramtowardsthehigher plagioclasecontainingtypesdueto theperthiticexsolutionof K-feldsparandconsequentinherentoverestimationf theabundanceof plagioclase. Keywords:Rietveld,XRD quantification,phaseanalysis,granitoid

The structure-sensitive and standardless phase quantification method based on a Rietveld analysis... more The structure-sensitive and standardless phase quantification method based on a Rietveld analysis of X-ray powder diffraction data was compared to some traditional techniques. It was found that the Rietveld-based method is at least equal, in several cases superior to the RIR technique, and can be a fast and simple substitute for the opticai modal analysis. At the same time it is shown that the points of a Rietveldbased rock classification, using the QAP rock classification of Streckeisen, can be erroneously shifted on the diagram towards the higher plagioclase containing types due to the perthitic exsolution of K-feldspar and consequent inherent overestimation of the abundance of plagioclase.

Journal of Solid State Chemistry

ABSTRACT

Materials Science Forum, 1994

Geologia Croatica, 2011

Potassium feldspars from different granitoids and gneisses of Papuk Mt. (Slavonia, Croatia) have ... more Potassium feldspars from different granitoids and gneisses of Papuk Mt. (Slavonia, Croatia) have been investigated by X-ray powder diffraction. Diffraction patterns classically observed as well as patterns calculated by Rietveld refi nement were compared and discussed. Triclinicity was calculated according to while the structural state of the feldspars was determined using the methods of and GO-DINHO & JALECO (1973). Results showed that the type of potassium feldspar depend on the investigated host-rock, indicating variation in the structural state from orthoclase, intermediate microcline to highly ordered microcline. Potassium feldspar megacrysts in biotite-granodiorites and monzogranites are intermediate microcline or orthoclase, while two-mica monzogranites contain low microcline. Gneisses contain low microcline and orthoclase in Brzaja Creek and low microcline in Djedovica Quarry. Classically observed and digital diffraction patterns calculated by the Rietveld refi nement method produced comparable results and provided a very good correlation of the results obtained by different methods. High triclinicity values of feldspars from investigated granitoid and gneiss samples from Papuk Mt. (Slavonia, Croatia) are in accordance with a high Al content in the T 1 o site and their fully ordered state indicates a slow(er) cooling-rate. Low triclinicity values, an Al content in T 1 o site around 0.60 and ordering index smaller than 0.80 can be interpreted as a result of relatively fast(er) cooling which allowed lower ordering of the potassium feldspar.