Journal of Nuclear Materials 457 (2015) 29–35

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Journal of Nuclear Materials

journal homepage: www.elsevier .com/ locate / jnucmat

Thermophysical properties of Ba1�xSrxMoO3(s)

http://dx.doi.org/10.1016/j.jnucmat.2014.10.0320022-3115/� 2014 Published by Elsevier B.V.

⇑ Corresponding author. Tel.: +91 22 25592417.E-mail address: manju_igcar@yahoo.com (M. Sahu).

Manjulata Sahu a,⇑, K. Krishnan b, M.K. Saxena a, Smruti Dash c

a Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, Indiab Fuel Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, Indiac Product Development Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India

a r t i c l e i n f o

Article history:Received 25 July 2014Accepted 21 October 2014Available online 29 October 2014

a b s t r a c t

Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid-solutions were synthesized by reduction of correspondingBa1�xSrxMoO4(s) and were characterized using X-ray diffraction (XRD). Thermal expansion behavior ofBa1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1) were investigated in the temperature range 298–873 K by high tem-perature X-ray diffraction (HTXRD). The average volume thermal expansion coefficient of Ba1�xSrx

MoO3(s) (x = 0, 0.4, 0.8 and 1) was found to be 2.83� 10�5, 2.20 � 10�5, 2.02 � 10�5 and 2.27� 10�5 K�1,respectively. Heat capacity of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8, 1) was measured with a heat flux-type differ-ential scanning calorimeter (DSC) in the temperature range 290–870 K. The specific heat of Ba1�xSrxMoO3(s)was found to increase with increase in concentration of strontium. The thermodynamic functions such asenthalpy increment, entropy and Gibbs energy functions of Ba1�xSrxMoO3(s) were also calculated.

� 2014 Published by Elsevier B.V.

1. Introduction

Irradiation of nuclear fuel in the nuclear reactor results in theproduction of large number of fission products and actinides. Forthe evaluation of performance and safety assessment of nuclearfuels, it is imperative to understand the behavior of the fissionproducts and the properties of their interactions products with fueland cladding material which in turn is dependent on large numberof parameters such as the type of fuel, oxidation potential, temper-ature, cladding material. It has been reported in literature that dis-solution of some of the fission products in the fuel matrix takesplace while the formation of separate oxide/metallic phase isobserved in case of other fission products [1–6]. The perovskite-type oxide (Ba,Cs, Sr)(U,Pu,Zr,RE,Mo)O3(s) phase has been observedin the fuel matrix. Initially barium forms BaUO3(s) and BaZrO3(s)phases in fuel which incorporates several radio nuclides such asSr, Cs, U, Pu, Mo and RE (rare earth). The composition of thesephases changes with mixed oxide fuel composition and burn-up.For instance, rare earths are found in the perovskite oxide phasesonly at very high burn up. ABO3 compounds exhibits ferro-electric-ity, ferromagnetism, superconductivity, thermal conductivity, ionicconductivity, piezoelectric, photo-catalytic and thermoelectricity.ABO3(s) compounds have simple structure and can flexibly accom-modate around 90 percent of the metallic elements of the periodictable. Due to compositional versatility of this structure, the proper-

ties of ABO3 compounds can be tuned by substitution, creation oforder or defect in its structures.

SrMoO3(s), BaMoO3(s) and their solid solutions have a numberof interesting properties. According to Goodenough’s classification[7], alkaline-earth molybdates containing Mo4+ (4d2) in three foldt2g orbital belong to the Pauli paramagnetic group, and have highelectron-transfer energy [8]. Hence, these oxides show metallicconductivities. Scholder [9] were first to report the synthesis ofBaMoO3(s) and SrMoO3(s) with perovskite structure by reductionof BaMoO4(s) and SrMoO4(s), respectively. Authors observed highstability of BaMoO4(s) and SrMoO4(s) even under reducing condi-tions. Kamata et al. [10] observed that reduction of BaMoO4(s) toBaMoO3(s) and SrMoO4(s) to SrMoO3(s) was possible at oxygenpotential below �386.4 kJ mol�1 and �351.1 kJ mol�1 respectivelyat 1473 K. Deluca et al. [11] proposed temperature more than1273 K is necessary to reduce BaMoO4(s) and SrMoO4(s) in plati-num boat under 15% H2/Ar atmosphere.

Crystallographic, electrical and magnetic properties of BaMoO3(s)and SrMoO3(s) have been well studied [8,12,13]. The thermoelectricproperties like electrical resistivity, Seebeck coefficient, and thermalconductivity of BaMoO3(s) have been studied by Kurosaki et al. [14].Yamanaka et al. [15,16] reported physical properties like thermalexpansion coefficient, melting temperature, elastic moduli, Debyetemperature, micro-hardness, heat capacity, and thermal conductiv-ity of SrMoO3(s) and also predicted the metallic behavior from thepositive temperature dependency of electrical resistivity. A fewresearch works on thermodynamic properties of BaMoO3(s) andSrMoO3(s) have been reported in the literature [17–25]. Agarwalet al. [17] measured enthalpy increment using drop calorimeter.

30 M. Sahu et al. / Journal of Nuclear Materials 457 (2015) 29–35

Dash et al. [18–21] studied the standard molar Gibbs energy offormation of BaMoO3(s) and SrMoO3(s) and phase diagrams ofBa–Mo–O and Sr–Mo–O systems. Brixner [26] measured XRD ofBa1�xSrxMoO3 and observed complete range of solid solutionsbetween BaMoO3(s) and SrMoO3(s) and also found metallic behaviorof these solid solutions from the determination of electrical property.However, thermodynamic properties of Ba1�xSrxMoO3(s) solid solu-tions have not been reported in the literature. The present study isfocused on the synthesis of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8,1) and measurements of their thermal expansion and heat capacityusing HTXRD and DSC, respectively.

2. Experimental

2.1. Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solutions

2.1.1. SynthesisBa1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solutions were

synthesized by the reduction of respective Ba1�xSrxMoO4(s) (x = 0,0.2, 0.4, 0.5, 0.8, 1).

2.1.1.1. Ba1�xSrxMoO4(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solu-tions. Ba1�xSrxMoO4(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solutionswere synthesized by complex polymerization method as discussedin our previous study [27]. The starting material used were BaCO3

(s) (99.999%, M/s Across Organics, Belgium), SrCO3(s) (99.99%, AlfaAesar, Lancaster), MoO3(s) (99.5%, Mallinck-rodt chemical works,New York), citric acid (99.7%, M/s Chemco fine chemicals, Mum-bai), ethylene glycol (99.0%, M/s Thomas Baker, Mumbai), selecti-pure HNO3 (M/s Merck Ltd., India) and NH3 solution (M/sChemco fine chemicals, Mumbai). SrCO3(s) and BaCO3(s) were pre-heated at 1123 K for 8 h and MoO3(s) was preheated at 573 K for4 h before using for synthesis.

2.1.1.2. TG–DTA. In order to identify the reaction temperatures forthe formation of Ba1�xSrxMoO4(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solidsolutions, respective precursor was analyzed with a thermo ana-lyzer (Mettler Thermoanalyzer, TA-1, Switzerland). The samplewas heated, under air flow rate of 0.05 dm3 min�1, at a heating rateof 10 K min�1 up to 1373 K. The reaction temperature for theformation of Ba1�xSrxMoO4(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solu-tions are shown in the Fig. 1. It also shows that the completedecomposition of all the precursors has taken place around 1073 K.

-100

-80

-60

-40

-20

0

mas

s lo

ss/m

g

BaMoO4(s)

SrMoO4(s)

Ba0.8

Sr0.2

MoO4(s)

Ba0.6

Sr0.4

MoO4(s)

Ba0.4

Sr0.6

MoO4(s)

Ba0.2

Sr0.8

MoO4(s)

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

0

10

20

30

Hea

t flo

w/M

icro

volt

T/K

Fig. 1. TG–DTA of precursors for the synthesis of Ba1�xSrxMoO4 (x = 0, 0.2, 0.4, 0.5,0.8, 1) solid solution.

The peaks of DTA curves are due to exothermicity of thecombustion reaction of precursors. TG plot shows single and con-tinuous step of decomposition. The precursor for compositionBa0.2Sr0.8MoO4(s) showed some peculiar behavior both in TG andDTA plot which could be due to the different types of complexationbehavior of metallic element in this composition. The precursorswere calcined at 1273 K for 6 h and the resulting white powderswere stored for the characterization.

2.1.1.3. Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solu-tions. Perovskite-type oxides of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4,0.5, 0.8, 1) were prepared by reduction of corresponding Ba1�xSrx

MoO4(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) oxides having scheelite-typestructure. In order to optimize the condition for reduction ofSrMoO4(s) and BaMoO4(s) to SrMoO3(s) and BaMoO3(s), the reduc-tion was tried separately with 8% H2(g) + Ar(g) mixture, pure H2(g)and in presence of carbon under Ar(g) by varying the temperature.The reduction in 8% H2(g) + Ar(g) and carbothermic reduction wastried in the temperature range 1173–1573 K for 10 h. But thereduction in pure H2 was carried out at 1293 K for 20 h. Theseproducts were stored for characterization by XRD.

2.1.2. Characterization2.1.2.1. X-ray diffractometry (XRD). Perovskite-type oxides Ba1�xSrx

MoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) and scheelite-type oxides: Ba1�

xSrxMoO4(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) were characterized using aSTOE theta–theta X-ray diffractometer employing graphite mono-chromatic Cu Ka radiation (k = 0.15406 nm). The scans were madein the range of 10� to 70�. The XRD pattern of pure BaMoO3(s) andSrMoO3(s) matches with the reported patterns [28,29]. The 2hpositions obtained for Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1)are shown in Fig. 2 and that for Ba1�xSrxMoO4 (x = 0, 0.2, 0.4, 0.5,0.8, 1) were matched with our earlier study [27].

2.1.2.2. Analysis of metallic elements by inductively coupled plasmamass spectrometry (ICPMS). An inductively coupled plasma time offlight mass spectrometer (ICP–TOF–MS), model: 8000R (GBC, Aus-tralia) was used for the determination of metallic elements inBa1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solutions. For thisstudy, quantitative amounts of solid solutions were digested inconcentrated nitric acid and dried. The final analyte solutions forICPMS were made with 1% nitric acid. The solutions were fed intoICPMS and the measured elemental compositions were used to findout the stoichiometry of Ba and Sr which is given in Table 1.

BaMoO3(s)

Ba0.8Sr0.2MoO3(s)

Ba0.6Sr0.4MoO3(s)

Ba0.5Sr0.5MoO3(s)

Ba0.2Sr0.8MoO3(s)

10 20 30 40 50 60 70

2Θ

Rel

ativ

e in

tens

ity (%

)

SrMoO3(s)

Fig. 2. XRD patterns of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.50, 0.8, 1) solid solutions.

Table 1The stoichiometry of Ba1�xSrxMoO3 (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solutionsdetermined from analysis of metallic content by ICPMS and non metallic oxygen byconverting it to CO2(g).

Slno.

Approximate stoichiometrysynthesized

Actual Stoichiometry determinedby ICPMS

1 BaMoO3 Ba1.048±0.053MoO3.17±0.1

2 Ba0.8Sr0.2MoO3 Ba0.779±0.068Sr0.198±0.045MoO3.1±0.09

3 Ba0.6Sr0.4MoO3 Ba0.568±0.026Sr0.456±0.015MoO3.32±0.1

4 Ba0.5Sr0.5MoO3 Ba0.473±0.04Sr0.49±0.057MoO3.07±0.09

5 Ba0.2Sr0.8MoO3 Ba0.194±0.013Sr0.811±0.012MoO3.09±0.07

6 SrMoO3 Sr0.961±0.02MoO3.02±0.09

M. Sahu et al. / Journal of Nuclear Materials 457 (2015) 29–35 31

2.1.2.3. Oxygen analysis. The oxygen content in Ba1�xSrxMoO3(s)(x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solutions were determined usingdeterminator supplied by M/s Chromatography and InstrumentsCompany (CIC), Vadodara, India. Stainless steels with different con-tent of oxygen supplied by M/s LECO Corporation (St. Joseph, MI,USA) were used as standards in present study. In this technique,the sample was fused in a graphite crucible in the presence ofnickel as a flux at a high temperature (�3000 K) in flowing inert(helium) gas. Under these conditions, oxygen gets released asCO(g) and trace amounts of CO2(s) depending on the oxygen con-tent in the sample. These released gases are carried away alongwith flowing helium and allowed to pass through hot copper oxide(CuO at 773 K) catalyst column, where CO(g) also gets converted toCO2(g). The total CO2(g) released was determined by IR detector.The elaborate procedure and description of instrument used isgiven by Ramanjaneyulu et al. [30]. The oxygen stoichiometry forBa1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) were calculated fromthe determined oxygen amount and are also given in Table 1.

2.1.3. Thermal expansion measurementsThe axial and volume thermal expansion measurements of

Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1) were carried out using STOEdiffractometer under reduced pressure (10�8 bar) with HDK-2.4Buhler high temperature attachment described by Keskar et al.[31]. The high temperature XRD patterns were recorded in thetemperature range of 298–873 K. Each sample was heated at aninterval of 100 K and equilibrated for 15 min at each temperaturebefore XRD measurement. The unit cell lattice parameters weredetermined from the XRD data obtained at each temperature.The refined lattice parameters (within an accuracy of ±0.001 Å),were calculated by the method of least squares using a computerprogram by Wadhawan [32].

2.1.4. Heat capacity measurementsHeat capacity Co

p;mðTÞ measurements of Ba1�xSrxMoO3(s) (x = 0,0.4, 0.8 and 1) were carried out using a heat flux-type differentialscanning calorimeter (model number DSC 823e/700 of M/s. MettlerToledo GmbH, Switzerland) in the temperature range 290–870 K.Temperature calibration was performed by determining meltingpoint of In, Zn and Pb. Similarly the heat flow calibration was per-formed by measuring enthalpies of phase transition of above men-tioned elements. Heat capacity measurements were carried out inthe temperature range 290–870 K employing heating rate of10 K min�1. The entire temperature range was divided into threesegments (283–473 K, 453–673 K and 653–873 K) to ensure goodthermal equilibrium. High purity gas mixture 4%H2–Ar was passedat a flow rate of 0.05 dm3 min�1 over the sample. A thin disc of sap-phire was used as the heat capacity standard. For measurement ofCo

p;mðTÞ, classical three-step method was used for blank, sapphireand sample runs in a continuous heating mode. The first step ofeach run was an isothermal one for fifteen minutes at an initialtemperature; the second step was a dynamic one with a heating

rate of 10 K min�1 and the final step was another isothermal onefor fifteen minutes at the final temperature. 70–80 mg of powdersamples of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1) were pelletisedand loaded in 40 ll Al pan and used for heat capacity measure-ments. The values of specific heat capacity were calculated usingfollowing equation [33]

CopðTÞsample ¼

HFsample � HFblank

HFref � HFblank

� �Mref

Msample

� �Co

pðTÞref ð1Þ

where HFblank, HFref and HFsample represent heat flow during theblank, sapphire and sample (Ba1�xSrxMoO3 (x = 0, 0.4, 0.8 and 1))runs, respectively; Co

pðTÞsample and CopðTÞref represent the specific heat

capacity of the sample and reference material (sapphire), respec-tively; and Mref and Msample represent the mass of the referenceand the sample respectively.

3. Results and discussion

3.1. Reduction condition of Ba1�xSrxMoO4 (x = 0, 0.2, 0.4, 0.5, 0.8, 1)solid solution

It was observed that SrMoO3(s) could be prepared using all thethree reduction conditions mentioned in the experimental section.However, pure BaMoO3(s) phase could not be prepared by usingeither by reduction in 8%H2(g) + Ar(g) atmosphere or carbothermicreduction. The product obtained in 8%H2(g) + Ar(g) is biphasic mix-ture of BaMoO3(s) + BaMoO4(s) but the compound BaMoO4(s)remains unchanged after carbothermic reduction. Pure BaMoO3(s)was formed only when BaMoO4(s) was loaded into a leak tightquartz-tube, heated at 1293 K under pure H2(g) at a flow rate of10 K min�1 for 20 h. The observed color of BaMoO3(s) andSrMoO3(s) were black and wine red, respectively. Hence, Ba1�xSrx

MoO3 (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid solution was prepared onheating the respective molybedate under pure H2(g) at 1293 Kfor 20 h. The reduction of Ba1�xSrxMoO4(s) to Ba1�xSrxMoO3(s) forx = 0.2, 0.4, 0.5, 0.8 can be described by the following reaction:

Ba1�xSrxMoO4ðsÞ þH2ðgÞ¢ Ba1�xSrxMoO3ðsÞ þH2OðgÞ ð2Þ

The color of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solidsolutions prepared in this study, was found to change from black-ish to wine reddish with decreasing barium content. The latticeparameters for these solid solutions at room temperature havebeen calculated from the XRD peaks and plotted as a function ofconcentration of SrMoO3(s) in the solid solution as shown inFig. 3. The plot followed Vegard’s law thereby confirming the for-mation of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solidsolutions.

3.2. Indexing cell parameters of Ba1�xSrxMoO3 (x = 0, 0.2, 0.4, 0.5, 0.8,1)

All the samples of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1)showed well crystalline structure and are indexed in the cubic sys-tem as shown in Fig. 2. No phase impurity was found. The com-puted room temperature lattice parameters, unit cell volume anddensity of cubic BaMoO3(s) and SrMoO3(s) are listed in Table 2and these values are in good agreement with that reported in theliterature [28,29]. Density of the unit cell was derived as per ourprevious study [34]. Similarly the lattice parameters for Ba1�xSrx

MoO3(s) (x = 0.2, 0.4, 0.5, 0.8) were refined by least square methodusing program by Wadhawan [32]. The observed and calculatedreflection for Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) along withtheir indices are given in Table 3. Fig. 3 shows the variation of lat-tice parameter of Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solidsolutions with Sr composition. It shows a deviation from Vegard’s

62.563.063.564.064.565.065.566.066.5

Ba 1-xSrx MoO3(x=0, 0.2, 0.4, 0.5,0.8,1) in the present study Fit of measured values in the present study Ba 1-xSrx MoO3 (x=0,0.25, 0.5, 0.75,1)[26]

Uni

t cel

l vo

lum

e (Å

)3

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.23.953.963.973.983.994.004.014.024.034.044.05

Mole fraction of SrMoO3(s)

Latti

ce p

aram

eter

(Å)

Fig. 3. A plot of linear lattice parameters (a) and unit cell volume (V) as a function ofmole fraction of SrMoO3(s) for Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solidsolutions.

32 M. Sahu et al. / Journal of Nuclear Materials 457 (2015) 29–35

law. The negative deviation was also predicted by Brixner [26]. Themeasured lattice parameters and unit cell volume of Ba1�xSrx

MoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) were fitted as a function of molefraction of SrMoO3(s) and the resulting equations are given as:

a ðÅÞ ¼ 4:0421� 0:0842 � xþ 0:0175 � x2 ð3Þ

V ðÅÞ3 ¼ 66:0432� 4:1119 � xþ 0:0175 � x2 ð4Þ

where ‘x’ is the mole fraction of SrMoO3(s) in the solid solutions.The reported lattice parameters and unit cell volumes [26] ofBa1�xSrxMoO4(s) (x = 0, 0.25, 0.5, 0.75, 1) are also shown in Fig. 3.The crystallographic data for Ba1�xSrxMoO3(s) (x = 0.2, 0.4, 0.5,0.8) has been reported for the first time.

3.3. Thermal expansion of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1)

The lattice parameters of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1)were calculated from diffraction angles and the miller indices atdifferent temperatures. The calculated linear lattice parametersand volume were fitted to a second order polynomial equation asper earlier study [27,34].

The thermal expansion coefficient (a) at any temperature T wascalculated from the formula

ðaÞ ¼ 1l298� dl

dTð5Þ

where l298 is the lattice parameter at room temperature and dl/dTthe slope of the curve at temperature T. The lattice parameters ofBa1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and 1) were best fitted to the secondorder polynomial expressions. These expressions are:

BaMoO3(s)

a ðÅÞ ¼ 4:0403þ 1:72� 10�5ðT=KÞ þ 1:779� 10�8ðT=KÞ2 ð6Þ

Table 2Crystal system and lattice parameter of BaMoO3(s) and SrMoO3(s).

Lattice parameters Tetragonal

SrMoO3(s)

Present study Literatu

a/Å 3.9741(9) 3.974c = 12.0308(39) c = 12.0

V/Å3 62.76(3) 62.76Z 1 1q/g cm�3 6.126 6.127

V ðÅ3Þ ¼ 65:9986þ 5:88� 10�4ðT=KÞ þ 1:329� 10�6ðT=KÞ2

� 2:459� 10�10ðT=KÞ3 ð7Þ

Ba0.6Sr0.4MoO3(s)

a ðÅÞ ¼ 4:0082þ 2:885� 10�5ðT=KÞ þ 1:193� 10�9ðT=KÞ2 ð8Þ

V ðÅ3Þ ¼ 65:1162� 2:9� 10�3ðT=KÞ þ 7:8970� 10�6ðT=KÞ2

� 4:4114� 10�9ðT=KÞ3 ð9Þ

Ba0.2Sr0.8MoO3(s)

a ðÅÞ ¼ 3:9883þ 2:733� 10�5ðT=KÞ þ 1:187� 10�10ðT=KÞ2 ð10Þ

V ðÅ3Þ ¼ 64:0075� 2:05� 10�3ðT=KÞ þ 6:1365

� 10�6ðT=KÞ2 � 3:467� 10�9ðT=KÞ3 ð11Þ

SrMoO3(s)

a ðÅÞ ¼ 3:9661þ 2:494� 10�5ðT=KÞ þ 4:498� 10�9ðT=KÞ2 ð12Þ

V ðÅ3Þ ¼ 62:6032� 1:2700� 10�4ðT=KÞ þ 2:636

� 10�6ðT=KÞ2 � :380� 10�9ðT=KÞ3 ð13Þ

The variation of lattice parameters and unit cell volume as afunction of temperature for Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and1) are given in Table 4. The values of the linear (aa) and volume(aV) thermal expansion coefficients at different temperatures werecalculated using Eq. (5). These values are also given in Table 4. Theaverage linear (aa) and volume (aV) thermal expansion coefficientsin the temperature range 298–873 K were best fitted to a polyno-mial equation as a function of the mole fraction of SrMoO3(s) andare represented in Fig. 4.

Expressions for the average linear (aa) and volume (aV) thermalexpansion coefficients are given below:

aa ¼ ð9:14� 7:18 � xþ 5:47 � x2Þ � 10�6 ð14Þ

aV ¼ ð2:84� 2:42 � xþ 1:82 � x2Þ � 10�5 ð15Þ

where ‘‘x’’ is the mole fraction of SrMoO3(s) in the solid solutions.The values of average volume thermal expansion coefficient in thepresent study are close to that of ceramic nuclear fuels [35,36].

3.4. Heat capacity measurement

Heat capacity was measured for Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8and 1) in the temperature range 290–870 K. The heat capacity ofBaMoO3(s) and SrMoO3(s) are the mean values of four measure-ments. The error derived from the mean standard deviation forBaMoO3(s) and SrMoO3(s) was found to be within 1–2.5%, respec-tively. For each composition, the experimental molar heat capacityvalues in the complete temperature range were best fitted toA + BT + CT�2 equation. A, B, and C are constants and T is absolute

BaMoO3(s)

re [29] Present study Literature [28]

4.0469(11) 4.04020 c = 12.822(1) c = 12.821

66.28(3) 65.941 17.046 7.083

Tabl

e3

X-r

aypo

wde

rdi

ffra

ctio

nda

taof

Ba1�

xSr x

MoO

3(s

)so

lidso

luti

ons.

BaM

oO3(s

)B

a 0.8

Sr0

.2M

oO3(s

)B

a 0.6

Sr0

.4M

oO3(s

)B

a 0.5

Sr0

.5M

oO3(s

)B

a 0.2

Sr0

.8M

oO3(s

)Sr

MoO

3(s)

d ob

sd c

alI/

I oh

kl

d ob

sd c

alI/

I oh

kl

d ob

sd c

alI/

I oh

kl

d ob

sd c

alI/

I oh

kl

d ob

sd c

alI/

I oh

kl

d ob

sd c

alI/

I oh

kl

2.85

72.

858

11

02.

848

2.84

61

10

2.83

82.

839

11

02.

830

2.83

01

10

3.98

23.

986

10

03.

982

3.97

61

00

2.33

32.

334

11

12.

323

2.32

41

11

2.31

72.

318

11

12.

308

2.31

11

11

2.82

12.

819

11

02.

812

2.81

11

10

2.02

22.

021

20

02.

012

2.01

32

00

2.00

72.

007

20

02.

001

2.00

12

00

2.30

22.

301

11

12.

295

2.29

51

11

1.65

01.

650

21

11.

643

1.64

32

11

1.63

91.

639

21

11.

635

1.63

42

11

1.99

41.

993

20

01.

988

1.98

82

00

1.42

91.

429

22

01.

419

1.41

92

20

1.62

71.

627

21

11.

623

1.62

32

11

1.40

51.

406

22

0

Sys:

cubi

c,sp

ace

grou

p:Pm

3m(2

21)

,Cu

Ka

(k=

1.54

06Å

),fi

lter

:N

iSp

ace

grou

p:14

1/a

(88)

(k=

1.54

06Å

)a

=4.

042

Å,Z

=1,

a=

4.02

5Å

,Z=

1,a

=4.

014

Å,Z

=1,

a=

4.00

2Å

,Z=

1,a

=3.

986

Å,Z

=1,

a=

3.97

6Å

,Z=

1,M

wt:

281.

27,

Mw

t:27

1.38

4,M

wt:

261.

384,

Mw

t=

256.

413,

Mw

t:24

1.50

,M

wt:

231.

56,

Vol

um

e:66

.04

Å3,

Vol

um

e:65

.21

Å3,

Vol

um

e:64

.67

Å3,

Vol

um

e:64

.10

Å3,

Vol

um

e:63

.33

Å3,

Vol

um

e:62

.85

Å3,

q=

7.07

2g

cm�

3q

=6.

910

gcm�

3q

=6.

711

gcm�

3q

=6.

642

gcm�

3q

=6.

332

gcm�

3q

=6.

117

gcm�

3

Table 4Lattice parameters (a), volume (V), linear (aa) and volume (aV) thermal expansioncoefficients of Ba1�xSrxMoO3(s) (x = 0, 0.4 and 1) solid solutions in the temperaturerange 298–873 K.

T/K a (Å) V (Å3) aa � 106 (�106 K�1) aV � 105 (�105 K�1)

SrMoO3(s)298.15 3.9741 62.76 4.03 1.21373 3.9753 62.82 6.42 1.93473 3.9788 62.99 8.56 2.57573 3.9821 63.14 7.67 2.31673 3.9849 63.28 7.93 2.39773 3.9884 63.44 8.05 2.43873 3.9913 63.58 7.30 2.21

Ba0.6Sr0.4MoO3(s)298.15 4.0172 64.83 4.31 1.29373 4.0185 64.89 6.39 1.92473 4.0219 65.06 7.72 2.32573 4.0247 65.19 8.46 2.55673 4.0287 65.39 8.71 2.63773 4.0317 65.53 6.60 1.99873 4.034 65.65 5.73 1.73

Ba0.2Sr0.8MoO3(s)298.15 3.997 63.86 3.67 1.10373 3.9981 63.91 5.34 1.60473 4.0009 64.04 7.63 2.29573 4.0042 64.20 8.38 2.52673 4.0076 64.37 7.01 2.11773 4.0098 64.47 6.00 1.81873 4.0124 64.60 6.50 1.97

BaMoO3(s)298.15 4.0469 66.28 9.23 2.77373 4.0497 66.42 7.58 2.28473 4.0521 66.53 7.78 2.34573 4.056 66.73 9.76 2.94673 4.06 66.92 10.25 3.10773 4.0643 67.14 10.87 3.29873 4.0688 67.36 11.12 3.37

M. Sahu et al. / Journal of Nuclear Materials 457 (2015) 29–35 33

temperature. The values of these constants are given in Table 5.Heat capacity at 298.15 K for Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8 and1) was found to be 101.18, 102.68, 102.01 and 102.29 J K�1mol�1,respectively. The measured heat capacities of BaMoO3(s) andSrMoO3(s) along with that reported in the literature [14,15,17]and estimated in this study using data from Barin et al.[37] areshown in Figs. 5 and 6 respectively.

Fig. 5 shows that the heat capacity data of BaMoO3(s) measuredin this study along with that reported values by Agarwal et al. [17]

α V

-0.25 0.00 0.25 0.50 0.75 1.00 1.25

18

20

22

24

26

28

30

6.5

7.0

7.5

8.0

8.5

9.0

9.5

Mole fraction of SrMoO3 (s)

αa

exp

ansi

on c

oeffi

cien

ts 1

06 (K-1

)Av

erag

e v

olum

e th

erm

al

Fig. 4. A plot of average linear and volume thermal expansion coefficient as afunction of mole fraction of SrMoO3(s) for Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8, 1) solidsolutions.

Tabl

e5

The

coef

fici

ents

ofhe

atca

paci

ty,e

ntha

lpy

incr

emen

t,en

trop

yan

dG

ibbs

ener

gyfu

ncti

onof

Ba1�

xSr x

MoO

3(s

)(x

=0,

0.4,

0.8,

1).

Soli

dso

luti

ons

(Ba 1�

xSr x

MoO

3)

Co p;

mðTÞ

A+

BT+

CT�

2

(Jm

ol�

1K�

1)

[300

–870

K]

Ho mðTÞ�

Ho mð2

98:1

5Þ¼

DTþ

ET2þ

FT�

1þ

G(k

Jmol�

1)

[298

.15–

870

K]

So mðTÞ¼

Hlo

gðTÞþ

ITþ

JT�

2þ

K(J

mol�

1K�

1)

[298

.15–

870

K]

�G

o mðTÞ�

Ho mð2

98:1

5ÞT

�� ¼

Llo

gðTÞþ

MTþ

NT�

2þ

O

(Jm

ol�

1K�

1)

[298

.15–

870

K]

xA

BC�

10�

6D

E�

105

FG

HI

J�10�

6K

LM

N�

10�

6O

012

3.25

0.03

�2.

760.

123

2.0

2760

�47

.34

283.

850.

031.

38�

624.

5667

.65

0.07

42.

41�

114.

250.

411

8.90

0.03

1�

2.25

0.11

92.

022

50�

44.3

573

.83

0.03

11.

12�

604.

2671

.28

0.07

12.

42�

129.

62�

2.02

20.0

1.01

2.66

0.8

116.

390.

034

�2.

190.

116

2.0

2190

�43

.58

268.

040.

034

1.09

�59

8.0

69.0

20.

072

2.39

131.

19�

3.84

9.27

1.94

2.71

111

5.09

0.03

1�

1.95

0.11

52.

019

52�

42.2

426

5.05

0.03

10.

98�

591.

8972

.13

0.06

82.

40�

141.

65�

2.93

10.0

1.48

2.72

200 300 400 500 600 700 800 900 100080

90

100

110

120

130

140

150

160

C p,m

(T)/(

Jmol

-1K-1

)

T/K

Measured Cop,m of BaMoO3(s)

Agarwal et al[17] Co

p,m additive[37] Kurosaki et al[14]

Fig. 5. Heat capacity of BaMoO3(s) as a function of temperature.

34 M. Sahu et al. / Journal of Nuclear Materials 457 (2015) 29–35

and Kurosaki et al. [14]. It shows scattered heat capacity valuesreported by different authors, which might be due to use of differ-ent experimental methods and ambient gas. The standard errors ofthe polynomial fit for the heat capacity of BaMoO3(s) is 0.77 J K�1

mol�1 in the temperature range 290–870 K. It can be seen fromFig. 5 that present heat capacity data for BaMoO3(s) are in goodagreement with Agarwal et al. [17]. But the values deviate fromKurosaki et al. [14] and that estimated from Neumann–Kopp rule.However the room temperature heat capacity values are closer toNeumann–Kopp additive values.

Fig. 6 shows the heat capacity data of SrMoO3(s) measured inthis study along with that reported by Maekawa et al. [16] andAgarwal et al. [17]. The standard error of the polynomial fit for heatcapacity of SrMoO3(s) is 0.42 J K�1 mol�1. The present data forSrMoO3(s) are matching reasonably with that of Agarwal et al.[17]. But it deviates from the estimated as well as from Maekawaet al. [16].

The specific heat capacity of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8, 1)solid solutions were plotted in Fig. 7. It was observed that specificheat of these solid solutions increase with increase in the concen-tration of strontium from x = 0 to 1. This is attributed to the higherheat capacity of SrMoO3(s) than that of BaMoO3(s).

From fitted equations of heat capacity and entropy at 298.15 K,other thermodynamic functions such as enthalpy increment

200 300 400 500 600 700 800 900 100090

100

110

120

130

140

150

Measured Cop,m of SrMoO3(s)

Agarwal et al[17] Co

p,m additive[37] Yamanaka et al[15]

Cp,m

(T)/(

Jmol

-1K

-1)

T/K

Fig. 6. Heat capacity of SrMoO3(s) as a function of temperature.

200 300 400 500 600 700 800 900 10000.34

0.36

0.38

0.40

0.42

0.44

0.46

0.48

0.50

0.52

0.54

0.56

0.58

0.60

0.62

Co p

(T)/(

Jg-1K-1

)

T/K

SrMoO3 (s) Ba0.6Sr0.4MoO3(s) Ba0.2Sr0.8MoO3(s) BaMoO3(s)

Fig. 7. Comparison of specific heat capacity of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8, 1)solid solutions as a function of temperature.

M. Sahu et al. / Journal of Nuclear Materials 457 (2015) 29–35 35

HomðTÞ � Ho

mð198:15Þ, entropy SomðTÞ and Gibbs energy function

� GomðTÞ � Ho

mð298:15Þ� �

=T were calculated in the temperaturerange of 298.15–870 K. Entropies of Ba1�xSrxMoO3(s) (x = 0,0.18,0.38, 0.60, 0.81, 1) solid solutions were computed assuming idealsolution model. So

mðBa1�xSrxMoO3; s;298:15Þ was estimated by tak-ing So

mð298:15Þ for SrMoO3(s) and BaMoO3(s) in the stoichiometricratio from Dash et al. [18,19] and ideal entropy of mixing (DSmix,id).The relations used for the calculations of thermodynamic functionsare given as follows:

HomðTÞ � Ho

mð298:15Þ ¼Z T

298:15ðCo

p;mÞdT ð16Þ

SomðTÞ ¼ So

mð298:15Þ þZ T

298:15

Cop;mðTÞ

T

!dT ð17Þ

�Go

mðTÞ � Homð298:15Þ

� �T

� �¼ So

mðTÞ

�Ho

mðTÞ � Homð298:15Þ

� �T

ð18Þ

The computed thermodynamic functions for Ba1�xSrxMoO3(s)(x = 0, 0.4, 0.8, 1) are given in Table 5.

4. Conclusions

1. Ba1�xSrxMoO3(s) (x = 0, 0.2, 0.4, 0.5, 0.8, 1) solid-solutions weresynthesized by reduction of Ba1�xSrxMoO4(s) (x = 0, 0.2, 0.4, 0.5,0.8, 1) and were characterized using XRD.

2. Single phase cubic phase was observed for Ba1�xSrxMoO3(s)(x = 0–1) and the lattice parameter of solid solutions were foundto deviate slightly (negative) from Vegard’s law.

3. The thermal expansion coefficient of Ba1�xSrxMoO4(s) (x = 0,0.4, 0.8 and 1) solid solutions were measured by HT-XRD forthe first time.

4. The average volume thermal expansion coefficient of Ba1�xSrx

MoO3(s) (x = 0, 0.4, 0.8 and 1) was calculated.5. Heat capacity of solid solutions was measured by a heat flux-

type differential scanning calorimeter.6. The specific heat capacity data of Ba1�xSrxMoO3(s) (x = 0, 0.4,

0.8, 1) solid solutions were found to increase with increasingconcentration of SrMoO3(s). The specific heat capacity of perov-skite oxides found to be more than the corresponding scheeliteoxides.

7. Thermodynamic functions of Ba1�xSrxMoO3(s) (x = 0, 0.4, 0.8, 1)such as enthalpy increment, entropy and Gibbs energy func-tions were computed from the measured heat capacity.

Acknowledgments

Authors are thankful to Shri B.K. Nagar for the ICPMS analysis,to Dr. P.S. Ramanjaneyulu and Shri C.S. Yadav for carrying outoxygen analysis and Dr. Pankaj Patro for helping in reduction ofsamples. Authors are also thankful to Dr., B.S. Tomar, Head Radio-analytical Chemistry Division and Dr. K.L. Ramakumar, Director,Radiochemistry and Isotope Group for their encouragement andkeen interest in this work.

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