Manganese Disulfide (Hauerite) and Manganese Ditelluride. Thermal Properties from 5 to 350°K and Antiferromagnetic Transitions

The heat capacities of manganese disulfide and manganese ditelluride were determined by adiabatic calorimetry in the range 5–350°K. Lambda‐type transitions are present in both compounds with maxima at 47.93°K for MnS2 and at 83.0°K for MnTe2. Entropies, enthalpies, and Gibbs energy function values are calculated and tabulated. At 298.15°K they are: S°  =  23.88cal/mole⋅°K,H° − H0°  =  3384cal/mole,− [(G° − H0°) / T]  =  12.258cal/mole⋅°KS°=23.88cal∕mole⋅°K,H°−H0°=3384cal∕mole,−[(G°−H0°)∕T]=12.258cal∕mole⋅°K for MnS2 and 34.66, 4416, and 19.847 for MnTe2. The clearly cooperative entropy increments are only 0.71 cal/mole⋅°K for MnS2 and 0.80 for MnTe2. Available magnetic susceptibility data are interpreted in terms of zero‐field splitting of the 6S5/26S5∕2 state of the manganese 3d53d5 electrons. The resulting contributions to the heat capacity are evaluated. At 298°K the combined λ‐transitional and Schottky contributions to the entropy are 2.6 and 2.4 cal/mole⋅°K for MnS2 and MnTe2, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69763/2/JCPSA6-52-7-3820-1.pd

Experimental set-up of a thermal vacuum chamber for thermal model in-house correlation and characterization of the HYPSO hyperspectral imager

Space environment with changing temperatures and vacuum can affect the performance of optics instruments onboard satellites. Thermal models and tests are typically done to understand the optics performance within large space projects, but less often in nanosatellites projects. It is even more rarer for an optics payload inside a CubeSat platform, made by a third provider, to do functional tests on their optics during space environment test campaign. In this research, an in-house made vacuum chamber with the possibility to warm up (TVAC) the devices under tests, and wall-through transparency for optics experiments is set-up. In parallel, a thermal model of the HYPerspectral Small satellite for ocean Observation (HYPSO) Hyperspectral Imager (HSI) is developed. The HSI, which is a transmissive grating hyperspectral instrument ranged in the visible to near infrared wavelength, has been tested in TVAC. As thermal control is based on heating the device under test, a new method for fitting the thermal models inside vacuum chambers with only heating capability is proposed. Finally, the TVAC set-up and the thermal model fitting method have been demonstrated to be appropriate to validate the HSI thermal model, and to characterize the optics performance of HSI in vacuum and in the range of temperatures found inside the in-orbit HYPSO-1 CubeSat.Research Council of Norway | Ref. 223254Research Council of Norway | Ref. 270959Norwegian Space Agency and the European Space Agency | Ref. 4000132515Ministerio de Universidades | Ref. CAS21/00502Universidade de Vigo/CISU

Heat capacity and other thermodynamic properties of CoTe 2 from 5 to 1 030 K and of CoTe 2.315 from 300 to 1 040 K

The heat capacity of orthorhombic (marcasite-type structure) cobalt ditelluride has been measured from 5 to 1 030 K by adiabatic-shield calorimetry with alternate energy inputs and equilibrations. Above 900 K a marked increase in heat capacity occurs which probably signals a change in the composition of the CoTe 2 -phase towards higher tellurium content. Values at 298.15 and 1 000 K in J K −1 mol −1 of the heat capacity ( C p,m ), entropy [ S m ° (T) − S m ° (0)], and Gibbs energy function − [ G m ° (T) − H m ° (0)] T −1 are 75.23, 114.5, 49.93, and 132.4, 216.2, 139.17, respectively. Consistent with the metallic behavior of CoTe 2 , deviation of the heat capacity from the Debye T 3 -law was found at low temperatures. Comparison with the heat capacity of FeTe 2 shows a Schottky -like deviation with a maximum of 7.3 J K −1 mol −1 at 80 K and evidences the influence of the additional 3 d-electron in cobalt compared to iron. Heat capacity measurements were made on CoTe 2.33 to ascertain the existence range of the CoTe 2+ x -phase and the entropy of the associated structural disorder. Es wurde die Wärmekapazität des orthorhombischen Kobaltditellurids (Markasit-Typ) zwischen 5 und 1 030 K mittels adiabatisch abgeschirmter Kalorimetrie mit alternierender Energiezufuhr und Gleichgewichtseinstellung gemessen. Über 900 K tritt ein deutlicher Anstieg der Wärmekapazität ein, der möglicherweise einen Wechsel in der Zusammensetzung der CoTe 2 -Phase zu einem höheren Tellur-Gehalt anzeigt. Entsprechende Werte bei 298.15 bzw. 1 000 K in J K −1 mol −1 für die Wärmekapazität ( C p, m ), die Entropie [ S m ° (T) − S m ° (0)] und die Gibbs Energiefunktion − [ G m ° (T) − H m ° (0)] T −1 sind 75.23, 114.5, 49.93 bzw. 132.4, 216.2, 139.17. In Übereinstimmung mit dem metallischen Verhalten von CoTe 2 wurde bei niedrigen Temperaturen eine Abweichung der Wärmekapazität vom Debye 'schen T 3 -Gesetz gefunden. Ein Vergleich mit der Wärmekapazität von FeTe 2 zeigt eine Schottky -gemäße Abweichung mit einem Maximum von 7.3 J K −1 mol −1 bei 80 K; dies zeigt den Einfluß der zusätzlichen 3 d-Elektronen im Kobalt, verglichen mit Eisen. Es wurden Wärmekapazitätsmessungen an CoTe 2.33 durchgeführt, um den Existenzbereich der CoTe 2+ x -Phase und die Entropie der damit zusammenhängenden strukturellen Unordnung zu ermitteln.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41694/1/706_2004_Article_BF00810867.pd

Actinoid pnictides--I : Heat capacities from 5 to 950 K and magnetic transitions of U3As4 and U3Sb4. Ferromagnetic transitions

The heat capacities of triuranium tetraarsenide (U3As4) and triuranium tetraantimonide (U3Sb4), measured by adiabatic calorimetry over the temperature range 5-950 K, show sharp [lambda]-shaped transitions at 196.1 and 147.5 K, respectively. The maxima are related to the appearance of permanent magnetic moments below 198 and 148 K. Excess cooperative entropies associated with ferromagnetic ordering are tentatively estimated as 6.7 for U3As4 and 6.8 cal K-1 mole-1 for U3Sb4. These are larger than the two literature values reported for U3P4 (1.5 and 3.1 cal K-1 mole-1). The fact that these entropy of transition values are much smaller than would be expected from [Delta]St = R In (2J + 1) for the 3H4 ground term (J = 4) and that the observed heat capacities at high temperatures are much larger than would be expected from lattice plus dilational contributions are evidence of crystal field effects. The total electronic entropies to 950 K are estimated as 11.05 and 12.95 cal K-1 mole-1 for U3As4 and U3Sb4, respectively. Thermal functions for both U3As4 and U3Sb4 are integrated from the experimental data up to 950 K. At 298.15 K, the values of Cpo [So(T)-So(0)] and -{[Go(T)-Ho(0)]/T} in cal K-1 mole-1, are 44.82, 73.87 and 38.97, U3As4 and 44.98, 83.60 and 46.89, for U3Sb4.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23080/1/0000655.pd

Actinoid pnictides--II : Heat capacities of UAs2 and USb2 from 5 to 750 K and antiferromagnetic transitions

The heat capacities of uranium diarsenide (UAs2) and uranium diantimonide (USb2), with tetragonal structures of the anti-Cu2Sb-type, have been measured by adiabatic-shield calorimetry from 5 to about 750 K. Lambda-type transitions with maxima at 272.2 and 202.5 K for UAs2 and USb2, respectively, are related to maxima in the magnetic susceptibilities at 277 and 203 K, occasioned by transitions from antiferro- to paramagnetism in the compounds. Values of the heat capacities (Cp), entropies [S[deg](T) - S[deg](0)], and Gibbs energy functions -{[G[deg](T) - H[deg](o)]/T} at 298.15 K in cal K-1 mole-1 are 19.12, 29.41 and 15.05 for UAs2 and 19.16, 33.81 and 18.39 for USb2. Tentative resolutions of the cooperative magnetic heat capacities of UAs2 and USb2 lead to the magnetic entropies [Delta]S(mag) = 0.99 and 1.70 cal K-1 mole-1, respectively. The values for both are significantly lower than the spin-only magnetic entropy value R ln 3 = 2.18 cal K-1 mole-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22763/1/0000318.pd

Optisk gyroskop konsept ved bruk av koblet resonator optisk bølgeleder: simulering og fabrikasjon

Koblede koblede resonator optiske bølgeledere (CROW) har vist stort potensial som optiske gyroskoper, og oppnår følsomhet for ytelsen til navigasjonsgrad. Imidlertid er de bare overlegne over enkle ring resonatorer når tapet er lite. I denne oppgaven ble beregningsverktøy for å bestemme forplantningsmodus og konstant utviklet ved bruk av endelig differens frekvens domene (FDFD) i MATLAB og utvidet til å omfatte anisotrope materialer. Metodene viser god relasjon til litteraturen og til andre numeriske metoder som endelig elementmodellering med COMSOL. Verktøyene kan fremdeles utvikles videre for å øke nøyaktigheten og omfanget.Fremstillingen av bølgeledere, resonatorer og CROW ble utført ved hjelp av en maskeløs fotolitografisk prosess med PicoMaster 150PM laserskriveren. Prosessen led imidlertid av problemer med overutvikling og fabrikasjonsoptimalisering. Fremtidig arbeid bør enten prøve å optimalisere fabrikasjonsprosessen eller bruke andre metoder for å produsere bølgelederne

Thermodynamics of iron sulfides I. Heat capacity and thermodynamic properties of Fe9S10 at temperatures from 5 K to 740 K

Measurements of the heat capacity of Fe9S10 over the temperature range 5 K to 740 K reveal a first-order structural transition at 495 K and two higher-order transitions with maxima at 534 K and 591 K. The last two are of coupled magnetic and structural origin. The structural changes giving rise to the heat-capacity effects are identified, and the magnetic properties are interpreted in terms of these. The standard entropy at 298.15 K of (1/19)Fe9S10 is compared with those of (1/2)FeS and (1/15)Fe7S8. The origin of the higher molar entropy for the first compound is found to reside mainly in the higher electronic heat-capacity contribution. The thermodynamic properties for (1/10)Fe9S10 have been evaluated and the values of Cp, m ΔT0Sm, and ΔT0Hom are 6.171 · R, 7.598 · R and 1147.3 · R · K at 298.15 K and are 6.944 · R, 14.524 · R, and 4572.4 · R · K at 740 K. (R = 8.31441 J · K-1 · mol-1).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29435/1/0000516.pd

Low‐Temperature Heat Capacities and Thermodynamic Functions of Some Platinum and Palladium Group Chalcogenides. I. Monochalcogenides; PtS, PtTe, and PdTe

Heat capacities of platinum monosulfide, platinum monotelluride, and palladium monotelluride were measured in the range 5–350°K. They show the normal sigmoidal temperature dependence with no evidence of transitions or other anomalies. The derived heat‐capacity equations were integrated. Values of heat capacities, entropy and enthalpy increments, and of the free‐energy function are tabulated for selected temperatures. At 298.15°K, the third‐law entropies are 13.16 cal gfw—1 °K—1 for PtS, 19.41 cal gfw—1 °K—1 for PtTe, and 21.42 cal gfw—1 °K—1for PdTe. The new data on PtS have been correlated with existing decomposition‐pressure data to evaluate ΔHf, ΔFf, and ΔSf298.15°K. Entropies for other platinum‐metal monochalcogenides were estimated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69534/2/JCPSA6-35-5-1665-1.pd