G. Gigli

Mass Spectrometric Study of the Vaporization of Cuprous Chloride and the Dissociation Energy of Cu3Cl3, Cu4Cl4, and Cu5Cl5

The vapor phase in equilibrium with cuprous chloride has been studied using the Knudsen effusion‐mass spectrometric technique. The polymeric species Cu3Cl3, Cu4Cl4, and Cu5Cl5 were observed, the first two in comparable amounts. Partial pressures and heats of vaporization for each species were measured: 3 CuCl(s)→Cu3Cl3(g),   Δ H640o=33.7± 0.8 kcal/mole, 4 CuCl(s)→Cu4Cl4(g),   Δ H650o=34.6± 0.7 kcal/mole, 5 CuCl(s)→Cu5Cl5(g),   Δ H665o=41± 1 kcal/mole. The atomization energies for these molecules calculated on the basis of the Rittner ionic model are compared with the experimental values.

On the Thermal and Thermodynamic (In)Stability of Methylammonium Lead Halide Perovskites

The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid organic-inorganic solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodynamic stability of the materials towards decomposition, which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that all the materials decompose to the corresponding solid lead (II) halide and gaseous methylamine and hydrogen halide, and the decomposition is well detectable even at moderate temperatures (~60 °C). Our results suggest that these materials may be problematic for long term operation of solar devices.

Thermochemical properties of the gaseous molecules VO, VO2, and V2O4

The gaseous molecules VO, VO2, and V2O4 were characterized thermochemically from the study of various all‐gas equilibria carried out by means of the high temperature‐mass spectrometry. The bond dissociation energies here determined for VO and VO2 are compared and discussed with previous results, while the molecule V2O4 was clearly identified for the first time. The thermochemical results obtained are: D°0(VO)=625.5±8.5 kJ mol−1, ΔH°f,298(VO,g)= 133.2±8.5 kJ mol−1; D°0(VO2)=1 177±18 kJ mol−1, ΔH°f,298(VO2,g)=−174±14 kJ mol−1; D°0,at(V2O4)=2880±23 kJ mol−1, ΔH°f,298(V2O4,g)=−878±23 kJ mol−1.

Vaporization thermodynamics of MgB2 and MgB4

The vaporization behavior of MgB2 and MgB4 under thermodynamic conditions has been studied by the Knudsen effusion-mass spectrometry technique. In the temperature range explored (883–1154 K), magnesium borides are observed to decompose by loss of gaseous Mg only. The equilibrium pressures of Mg(g) have been measured during high-temperature decompositions involving MgB2/MgB4 and MgB4/MgB7 two-phase mixtures and the corresponding standard reaction enthalpies were determined. The decomposition temperatures for MgB2 and MgB4 were also inferred by the relevant Van’t Hoff plots.

Thermodynamic stabilities of intermediate phases in the Ca–Si system

Abstract Vaporization thermodynamics in the binary system calcium–silicon has been studied by Knudsen effusion-mass spectrometry and vacuum microbalance techniques. The equilibrium partial pressure of Ca(g) over the two-phase regions in the composition range 20–75at.% Si has been measured and the standard enthalpy changes for the appropriate vaporization reactions were determined from the temperature dependence of the measured vapor pressures. The standard reaction enthalpy changes were also evaluated by the third-law method using the pressure data in conjunction with estimated Gibbs energy functions. Standard enthalpies of formation of the calcium silicides were derived from the standard reaction enthalpy values at room temperature. The results obtained for ΔfH°298 were the following: Ca2Si=−56.1±3.1, Ca5Si3=−55.3±3.5, CaSi=−49.6±2.2, Ca3Si4=−40.6±1.5, Ca14Si19=−44.4±2.3, CaSi2=−37.8±1.6 all in kJ/mol atoms. The results for Ca2Si, CaSi and CaSi2 may be compared with previous measurements, all other results are first determinations.

Dissociation Energy of CuCl and Cu2Cl2 Gaseous Molecules

Using the mass spectrometric and double oven technique, the molecules CuCl(g) and Cu2Cl2(g) have been observed in the superheated vapors of cuprous chloride. From the study of the various gaseous equilibria, the atomization energies of CuCl(g) and Cu2Cl2(g), D0o(CuCl)=90.6± 1.1 and D0o(Cu2Cl2=225.8± 1.1 kcal/mole, were derived. Polymerization energies of CuCl to dimer, trimer and tetramer, and the energy of formation of Cu2Cl2(g) from trimer and tetramer were also determined.

Mass spectrometric study of the thermochemistry of gaseous EuTiO3 and TiO2

The gaseous molecule EuTiO3 has been investigated in a high temperature mass spectrometric study of vapors over the europium–titanium–oxygen system. From the enthalpy of reaction: EuTiO3(g)=EuO(g)+TiO2(g) and proper ancillary data, the atomization energy of this molecule has been determined. In addition, from the study of the gaseous exchange reaction: TiO2(g)+Eu(g)=TiO(g)+EuO(g) the dissociation energy of TiO2(g) has been derived and compared with previous results. The dissociation energies proposed are: D○0,at(EuTiO3) =2278±28 kJ mol−1 and D○0,at(TiO2) =1260±12 kJ mol−1.

Thermodynamic study of gaseous ternary europium–tungsten–oxygen molecules

In the course of a mass spectrometric Knudsen cell study of the vaporization of europium orthophosphate and mixtures of it with europium sesquioxide the molecules EuWO3, EuWO4, Eu2WO5, and EuW2O7 were observed in the vapors. From the study of a number of pressure independent equilibrium reactions the atomization energies of these ternary molecules have been determined. In addition, the dissociation energy of EuO was determined and compared with previous results. The results obtained are D°0(EuO) =111.6±1.7; D°0,at(EuWO3) =569.6±6.9; D°0,at(EuWO4) =714.6±6.5; D°0,at(Eu2WO5) =960.0±10.9; D°0,at(EuW2O7) =1276.3±9.0 kcal mol−1.

A mass spectrometric and density functional study of the intermetallic molecules AuBe, AuMg, and AuCa

The intermetallic molecules AuBe and AuCa were identified by means of the Knudsen-Effusion Mass Spectrometry technique in the high-temperature vapors produced by vaporizing Au-Be-Ca alloys of proper composition. The gaseous equilibria AuBe(g)+Au(g)=Au(2)(g)+Be(g) and AuCa(g)+Au(g)=Au(2)(g)+Ca(g) were studied in the temperature ranges 1720-1841 K and 1669-1841 K, respectively, by monitoring the partial pressures of all the species involved. The equilibrium data were analyzed by the third-law method, obtaining for the first time the dissociation energy D(0) ( composite function) of the two intermetallic species: D(0) ( composite function)(AuBe)=234.0+/-4.0 kJ/mol; D(0) ( composite function)(AuCa)=246.7+/-4.0 kJ/mol. These values are significantly higher than the recently published D(0) ( composite function) of the species AuMg (175.4+/-2.7 kJ/mol). Furthermore, the ionization energies (IE) of AuBe, AuMg, and AuCa were obtained by measuring the electron impact ionization efficiency curves, IE(AuBe)=7.5+/-0.3 eV, IE(AuMg)=6.7+/-0.3 eV, and IE(AuCa)=5.5+/-0.3 eV. Theoretical calculations were also carried out for these species by density functional theory methods (PW91 and BP86) used in conjunction with Stuttgart relativistic effective core potentials. Both functionals were found to perform very well in reproducing experimental D(0) ( composite function), IE, and molecular parameters.

Dissociation Energies of the Ga2, In2, and GaIn Molecules

The group III metal dimers Ga2 and In2 and the newly identified intermetallic molecule GaIn were investigated in a Knudsen cell-mass spectrometric study of the vapors over gallium–indium alloys. From the all-gas equilibria analyzed by the second-law and third-law methods the following dissociation energies were derived; D00 (Ga2)=110.8±4.9 kJ mol−1, D00 (In2)=74.4±5.7 kJ mol−1, D00 (GaIn)=90.7±3.7 kJ mol−1. The value here measured for the dissociation energy of In2 is discussed and compared with a previous experimental determination and with the results of more recent theoretical investigations.