Kinetics of perlite glasses degassing: TG and DSC analysis

Kinetics of dehydration is one of the important characteristics of natural water-bearing glasses. This study deals with the simultaneous TGA/DSC of perlites. The dehydration profiling of natural perlite samples from Eastern Rhodopes (Bulgaria) and a pitchstone from the Eastern Transbaikal region (Russia) has been obtained by the use of a thermal balance. Initial water content in samples varied between 4.0 to 6.5 wt% H₂O. In pitchstone TG and DTG signals indicate two degassing maxima at temperatures of 220 and 290 °C. The peaks in the DTG signal mimic those in DSC signal. Perlitic water is driven out smoothly under heating over a wide ränge of temperatures from 140 to 700°C up to the glass transition temperature (Tg). The glass transition temperature has been determined independently from viscosity measurement using a micropenetration method. In slowly cooled perlites DTG and DSC Signals have one distinct peak which extends from 140 up to 800 to 850 °C. In fast cooled perlites DTG and DSC signals often exhibit two distinct peaks at around 200 to 450 and 600 to 700 °C. The temperature ränge of DTG and DSC peaks is wider than in slowly cooled perlites. The enthalpy effect of perlite glass dehydration at 200 to 300 °C has the enthalpy value of 55 to 75 kJ/mol, which is much larger than the enthalpy value (30 to 25 kJ/mol) of water evaporation at these temperatures. The additional thermal effect of periite dehydration may be associated with the water desorption reaction and water vapour expansion in microcracks

Unusual weak magnetic exchange in two different structure types: YbPt2_2Sn and YbPt2_2In

We present the structural, magnetic, thermodynamic, and transport properties of the two new compounds YbPt$_2$Sn and YbPt$_2$In. X-ray powder diffraction shows that they crystallize in different structure types, the hexagonal ZrPt$_2$Al and the cubic Heusler type, respectively. Despite quite different lattice types, both compounds present very similar magnetic properties: a stable trivalent Yb$^{3+}$, no evidence for a sizeable Kondo interaction, and very weak exchange interactions with a strength below 1K as deduced from specific heat $C(T)$. Broad anomalies in $C(T)$ suggest short range magnetic ordering at about 250mK and 180mK for YbPt$_2$Sn and YbPt$_2$In, respectively. The weak exchange and the low ordering temperature result in a large magnetocaloric effect as deduced from the magnetic field dependence of $C(T)$, making these compounds interesting candidates for magnetic cooling. In addition we found in YbPt$_2$In evidences for a charge density wave transition at about 290K. The occurrence of such transitions within several RET$_2$X compound series (RE = rare earth, T = noble metal, X = In, Sn) is analyzed.Comment: 16 pages, 7 figure

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8_8Ge40+x_{40+x}Ni6−x_{6-x}

One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present a combined neutron scattering and theoretical investigation of the lattice dynamics in the type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe a strong hybridization between phonons of the Ba guest atoms and acoustic phonons of the Ge-Ni host structure over a wide region of the Brillouin zone which is in contrast with the frequently adopted picture of isolated Ba atoms in Ge-Ni host cages. It occurs without a strong decrease of the acoustic phonon lifetime which contradicts the usual assumption of strong anharmonic phonon--phonon scattering processes. Within the framework of ab-intio density functional theory calculations we interpret these hybridizations as a series of an ti-crossings which act as a low pass filter, preventing the propagation of acoustic phonons. To highlight the effect of such a phononic low pass filter on the thermal transport, we compute the contribution of acoustic phonons to the thermal conductivity of Ba$_8$Ge$_{40}$Ni$_{6}$ and compare it to those of pure Ge and a Ge$_{46}$ empty-cage model system.Comment: 10 pages, 10 figure

Low-temperature structural investigations of the frustrated quantum antiferromagnets Cs2CuCl(4-x)Br(x)

Powder X-ray diffraction (PXRD) and single-crystal neutron scattering were used to study in detail the structural properties of the Cs2CuCl(4-x)Br(x) series, good realizations of layered triangular antiferromagnets. Detailed temperature-dependent PXRD reveal a pronounced anisotropy of the thermal expansion for the three different crystal directions of the orthorhombic structure without any structural phase transition down to 20 K. Remarkably, the anisotropy of the thermal expansion varies for different $x$, leading to distinct changes of the geometry of the local Cu environment as a function of temperature and composition. The refinement of the atomic positions confirms that for x=1 and 2, the Br atoms occupy distinct halogen sites in the [CuX4]-tetrahedra (X = Cl, Br). The precise structure data are used to calculate the magnetic exchange couplings using density functional methods for x=0. We observe a pronounced temperature dependence of the calculated magnetic exchange couplings, reflected in the strong sensitivity of the magnetic exchange couplings on structural details. These calculations are in good agreement with the experimentally established values for Cs2CuCl4 if one takes the low-temperature structure data as a starting point

Physical properties of single-crystalline Ba 8 Ni 3.5 Ge 42.1 h 0.4

Clathrates are candidate materials for thermoelectric applications because of a number of unique properties. The clathrate I phases in the Ba-Ni-Ge ternary system allow controlled variation of the charge carrier concentration by adjusting the Ni content. Depending on the Ni content, the physical properties vary from metal-like to insulator-like and show a transition from p-type to n-type conduction. Here we present first results on the characterization of millimeter-sized single crystals grown by the Bridgman technique. Single crystals with a composition of Ba8Ni3.5Ge42.1h0.4 show metallic behavior (dp/dT > 0) albeit with high resistivity at room temperature [p (300 K) = 1 mOhm cm]. The charge carrier concentration at 300 K, as determined from Hall-effect measurements, is 2.3 e-/unit cell. The dimensionless thermoelectric figure of merit estimated at 680 K is ZT ~ 0.2. Keywords Clathrates - thermoelectric material - intermetallic compound - nicke

Reports from the United States of North America on railroads, steamship travel, banks and other public undertakings by Franz Anton Ritter von Gerstner and Description of a Journey through the United States of North America by Clara von Gerstner, née von Epplen-Härtenstein Translated, with an introduction, by Steven Rowan

What follows contains a translation of the Berichte aus den Vereinigten Staaten von Nordamerika… [= Reports from the United States of North America] by Franz Anton Ritter von Gerstner, published in Leipzig in August 1839, and posted on the website of “austrian literature online.” It is the companion piece to two other classics of contemporary travel literature, one of them Ritter von Gerstner’s massive description of the transportation system of the United States published by F. A. von Gerstner’s assistant, Ludwig Klein,1 as well as the touching detailed travel narrative of his widow, Clara von Gerstner, Beschreibung einer Reise durch die Vereinigten Staaten von Nordamerika (Leipzig, 1842) [=Description of a Journey through the United States of North America]. A copy of this book, almost loved to pieces, is part of the rare book collection of the Saint Louis Mercantile Library at the University of Missouri-St. Louis, and is available online from Hathitrust. The two texts presented here will enable the proper telling of a remarkable if ultimately sad story, preserving and completing an account that is worth preserving for both a European and an American audience. Clara von Gerstner, née von Epplen-Härtenstein, the widow of Franz Anton Ritter von Gerstner, a noted railroad engineer who died in 1840 in Philadelphia, Pennsylvania, while inspecting American railroads on what was generally seen as a mission on behalf of Tsar Nicholas I of Russia. Although the description of Frau von Gerstner is worth reading in its own right, it will also serve as a companion to her husband’s survey of American transportation published posthumously as Die innern Communicationen der Vereinigten Staaten von Nordamerika, 2 vols. (Vienna: L. Förster’s artistische Anstalt, 1842-1843), as well as to Michel Chevalier’s earlier Histoire et description des voies de communication aux États-Unis et des travaux d’art qui en dépendent, 2 vols. (Paris: Librairie de Charles Gosselin, 1840-41, engraved plates 1843).2 This translation is based on two German sources: an original imprint copy in the Saint Louis Mercantile Library at the University of Missouri-St. Louis, and the online text supported by the Hathitrust Digital Library. I have also referred to the partial translations on South Carolina and of Alabama published in regional historical journals by Frederic Trautmann, as remarked in footnotes, but I looked at this resource only after completing my own translation. I also made use of some of Professor Trautmann’s footnotes on local figures, as indicated there. Clara von Gerstner’s travel narrative was well-received at the time of its publication, and its presence in many libraries shows that it was widely purchased and read although never translated or republished in the United States at the time — which is surprising in view of the usual popularity of similar accounts in America. One major reason might be the fact that the author ended up accepting current arguments by Southern defenders of the institution of slavery. At this moment, Clara von Gerstner’s own story outside of what is contained in this memoir is almost totally obscure. The LDS record of her marriage with Franz Anton von Gerstner in Frankfurt am Main shortly before their departure for America is almost the only independent evidence on her life and ancestry, along with her own casual mention of the birth of her daughter Philadelphia (no date) in autumn, 1839, her husband’s death on 12 April 1840, and her return from New York to Liverpool by packet sailing ship a month later.3 All that remains is the completion of her revision of the text in May, 1841, and the book’s printing in Leipzig in 1842. The attached text is identical in pattern to the published book, with the sole exception of eliminating the summaries of the text at the start of each chapter, which largely recapitulate those in the table of contents. I indicate the original pagination by giving the page numbers in brackets [ ]. The detailed introduction to the English edition of Ritter von Gerstner’s survey, “The Long Road to a Terminus in America: The Railroad Engineering Career of Franz Anton von Gerstner” by Frederick C. Gamst, provides a story of social advance in the Austrian Empire and its ambiguous end represented by a man whose career ended in failure as well as death.4 Franz Anton’s father, Franz Joseph Gerstner (1756-1832), had risen under the radical Holy Roman Emperor Joseph II (ruled 1780-90) and his successors to a unique height in Bohemia as a leading mathematician, engineer, and entrepreneurial educator. Beginning life as the son of a harness maker, he was raised to the hereditary nobility as a Ritter (“knight”) for pioneering new techniques of surveying. In 1806, he launched the Polytechnic Institute of Prague, the first such institution in Central Europe. As an engineer, he promoted the building of a railroad instead of a canal to join the Danube and the Moldau (Vltava), potentially linking the North Sea with the Black Sea and the Mediterranean. His name as well as his coat of arms remained a reminder of his origin from a family close to the soil, since Gerste is German for barley, a major ingredient in beer. Franz Anton von Gerstner (1796-1840) was raised in Prague and educated partly there as well as in the imperial capital of Vienna. When plans to join the Danube and Moldau were revived after the Congress of Vienna, he became the head of a project to construct a rail line from Budweis to Linz, modeled on the English Stockton & Darlington Railroad. A visit to England was like a religious conversion to him, and in 1822 he intended to build a line that would be serviced by horses at first, but which would eventually use locomotives, meaning that it had to built heavier than would otherwise be the case. Receiving an Imperial commission to construct a railroad between Budweis and Mauthausen, he began a pattern that would be repeated in the course of his professional life: he built a line that was greatly over budget and tardy in completion. He had no talent in dealing with his workers, and there were repeated work delays and stoppages as a result. Regular freight service on Gerstner’s northern end of the railroad began on 2 April 1829, but another director completed the line, to Linz, as a horse-drawn railroad in 1832. Before completing his portion of the Bohemian line, Franz Anton von Gerstner had married his first wife, Josephine marquise de Lambolin, born in 1805, in St. Stephan’s Cathedral in Vienna in 1825, but she died in 1835 in St. Petersburg, Russia, which had become his new center of action. This match might indicate that he was determined to reinforce his status as the member a relatively new noble line (his father had been the first ennobled): his wife was from a French émigré noble family that had found refuge in Austria in the era of the French Revolution and its Napoleonic aftermath. His second wife’s descent from the noble family of von Epplen-Härtenstein, with long service to the princely family of Thurn und Taxis, hinted a similar strategy.5 With his railroad in the Austrian Empire in other hands, Franz Anton Ritter von Gerstner made further visits to Britain to reinforce his notions of how railroads were made in the homeland of the craft. He now turned his attentions to Russia, arriving in St. Petersburg in August 1834. He proposed a grandiose plan for railroads all over the Empire tied with a remunerative role for himself, but he sought to extend his projected line from St. Petersburg to Moscow (and eventually to Nizhny Novgorod [Gorky in the Soviet era]). In the end, the project developed much as the Budweis line, mired in cost overruns and labor problems. His construction took place in 1836 and 1837, interrupted by frequent visits to other railroad sites in Belgium and England. His railroad, opened on 30 October 1837, would never develop beyond the status of a demonstration, and it became a Sunday excursion line from St. Petersburg to the Tsar’s residence at Zarskoe Selo. If his project had any long-term impact, it was his adoption of a wider gauge that would approximate that later adopted for Russian railroads. F. A. von Gerstner’s Report, the first of the two texts that follow, is a clear, comprehensible review of the lessons he felt he had learned from his inspection of American transportation. Like his strict contemporary Michel Chevalier, he argued that the American builders of railroads showed clear solutions to problems besetting European railway systems. The American locomotive and the American passenger car were, to him, advances over European designs, leading to a dramatic reduction in costs and improvement in safety. His long research in the American South on the use of wood for fuel over coke promised, in his eyes, promised dramatic savings. Above all, the energy and enterprise of American engineers was celebrated by Gerstner, as it was by Chevalier. The principal monument of his visit to America would be the publication of his analysis of American railroads compiled from his research reports by his assistant Ludwig Klein and published in German in two volumes in 1842 and 1843. The circumstances of its compilation, without a narrative thread, has caused it to be regarded as a collection of data with little charm for the reader. The collection of reports (Berichte) published during his last full year of life, however, provides insight into every aspect of the ingredients of American enterprise, including financing and education. The lively style of the Reports is in drastic contrast with the rather deadly survey that his assistant Klein compiled and published in Germany after the author’s death. Written for the popular press, the Reports provide a vision of the United States as a booming economy that had to be taken seriously by Europe. Although Gerstner would not live to see it, Americans such as George Washington Whistler would play a major supporting role in the modernization of the Russian economy. Finally, the last of the ten Reports, composed during his seaside Kur in Cape May, New Jersey, included detailed pleas defending his work in Austria as well as in Russia. It appears that the Tsar had decided to commission his own review of American transportation, signaling that F. A. von Gerstner could no longer regard himself as the Tsar’s agent in the United States.6 He gave signs of settling down in Philadelphia as a permanent resident, although this was perhaps simply a sign that his European prospects had died. This probably contributed to his distress and accelerated the collapse of his health and a “terminus” in Philadelphia. Gerstner, who still enjoyed status in America as a pioneer builder of railroads despite his twofold fiascos in Bohemia and Russia, had set out to make a grand tour of the booming railroads of the United States. Shortly before his departure, he married his second wife, Clara von Epplen-Härtenstein, the daughter of the representative of the Thurn und Taxis princely family’s interests at Germany’s General Post Office in Frankfurt am Main. Gerstner undertook this journey despite chronic poor health, and when he departed the Old World in 1838 he was fated never to return. The travel diary of his young wife, recast as a travel narrative, is a worthy memorial of this last journey, deserving attention in its own right. This is although even the most recent scholarship tends to see Clara von Gerstner’s popular and wellreceived account as a simple reflection of her engineer husband’s interest in seemingly “non-feminine” subjects.7 The only thorough study of German women’s travel narratives in the period views Clara von Gerstner’s account entirely in terms of her husband, but I would hold that the elective affinities (Wahlbekanntschaften)between the two goes beyond mere mimicry. Her apparently lively interest in such subjects as the Tredegar Iron Works in Richmond reflects genuine involvement in technical processes [258-262]. Also, as a Catholic, she appeared fascinated by convents, churches, and charitable institutions. She also reflected the thenfashionable interest in American penitentiaries as instruments for correcting bad conduct famously recorded by Alexis de Tocqueville and Gustave de Beaumont, and more recently seized upon by Michel Foucault and his French intellectual entourage. Since F. A. von Gerstner’s tour of the United States was cut short by his chronic ill health, leading him back to Philadelphia and a seashore “cure” at Cape May, New Jersey, the part of the United States he actually saw in detail consisted of the region of the Erie Canal (in the dead of winter), the Mississippi and Ohio Rivers, the environs of Boston and Philadelphia, but mostly the slave-owning South. Here Clara von Gerstner had a real transformation of her previous feelings in encountering slavery and the economy of the “Deep South.” She came to America with a preconceived horror of slavery, and the ubiquitous presence of Negroes as servants on a troubled Atlantic crossing in winter and in New York City was novel and disturbed her. When she first came to deal with slavery in the “Border South,” she was offended by happening upon an auction of household goods that incidentally included a young female slave. There is a brief moment when she visits a convent of black nuns in Baltimore, conversing with one of the nuns in French, and recording her fascination with their clothing and exotic appearance [237-239]. Then her attention shifts to a convent of white nuns, and she was charmed by experiencing a female community in an idyllic if sheltered world [240-243; 337-341]. But in Maryland and northern Virginia, she felt that she was viewing a slave regime in the process of dissolution. Slaves were being “sold south,” slaveholding seemed to be dwindling, and the promise of resettlement of former slaves in Liberia promised to bring the institution to an end in a region where poor white people could be used to raise tobacco and other local crops. In response, it might be noted that the slaves themselves, chained together in “coffles” were led to the more severe discipline of the land of “King Cotton.” In Charleston, she encountered the leaders of the South still mobilized in a “commercial convention” in the aftermath of the Nullification Crisis of a few years before, and she heard the young Alexander Hamilton Stephens (future Vice President of the Confederacy) excoriating the gathering for their lack of substantial action [296]. Soon she would integrate this with the notion that the soils of cotton plantations produced noxious miasmas that only Negro workers could tolerate during the summer months. During this period of the year, when almost the entire planter class migrated to the North to escape contagion, slaves were left to the tender mercies of the equally marginal white “overseer class.”8 The America Clara von Gerstner observed was a society in rapid and visible reorganization, with the remnants of the Native American tribes being moved to the West, doomed to be pushed again ever further by advancing white farmers [108]. To her eyes, the Border South would soon have many fewer Negroes and would be inclined to abandon slavery [226], and only the Cotton South would remain as the core of probable secession. But Clara also saw positive things about the South besides the beauty of its flowers and its trees draped with Spanish moss. She enjoyed Negro singing, and when dressed in their Sunday best she thought them delightful to observe. She came to the conclusion that white people in the North had done their best to segregate Negroes out of their lives, while people of the South interacted with them more openly and humanely [273]. She still felt that Negroes were incapable of more than marginal improvement, but in this way, she remained what she had always been, a European aristocrat in America viewing the lower classes from above and outside. In the final phase of her visit, she sought to settle down and create a home for herself, her ailing husband, and her new daughter, whom she had had baptized with the name of her favorite American town, Philadelphia. We see her trying to hire servants and keep them subordinate, although it was difficult to get the kind of servants-for-life that she expected in her heart as a noble. She was distressed by the fact that the many newspapers she and her husband felt compelled to peruse in the morning came to the table only after they had been read by “the help” [446]. The death of Franz Anton Ritter von Gerstner on 12 April 1840 cut Clara von Gerstner’s life in America short, and she departed for Europe soon after burying her beloved husband in Philadelphia, where local railroad enthusiasts have seen to the maintenance and eventual replacement of his stone marker. While she had come to America on the largest of seagoing steamships, she would return on a small sailing ship, a packet boat from Philadelphia to Liverpool, with a ticket that was half the price of steamer passage [455]

Crystal growth of copper-rich ytterbium compounds: The predicted giant unit cell structures YbCu4.4 and YbCu4.25

Two new phases YbCu4.4 and YbCu4.25 are found as a result of careful phase diagram investigations. Between the congruent and peritectic formation of YbCu4.5 and YbCu3.5, respectively, the phases YbCu4.4 and YbCu4.25 are formed peritectically at 934(2)degC and 931(3)degC. Crystal growth was realised using a Bridgman technique and single crystalline grains of about 50-100 10^{-6}m were analyzed by electron diffraction and single crystal X-ray diffraction. Due to the only slight differences in both compositions and formation temperatures the growth of larger single crystals of a defined superstructure is challenging. The compounds YbCu4.4 and YbCu4.25 fit in Cerny`s (J. Solid State Chem. 174 (2003) 125) building principle {(RECu5)n(RECu2)} where RE = Yb with n = 4 and 3. YbCu4.4 and YbCu4.25 base on AuBe5/MgCu2-type substructures and contain approximately 4570 and 2780 atoms per unit cell. The new phases close the gap in the series of known copper-rich rare earth compounds for n = 1, 2 (DyCu3.5, DyCu4.0) and n = 5 (YbCu4.5, DyCu4.5)