High-temperature heat capacity of Pb8La2(GeO4)4(VO4)2 in the range 320–1000 K

Abstract

The oxide compound Pb 8 La 2 (GeO 4 ) 4 (VO 4 ) 2 with an apatite structure has been synthesized by a ceramic method. The effect of temperature on the molar hear capacity of polycrystalline samples in the temperature range 320-1000 K has been studied by differential scanning calorimetry. The results have been used to calculate the thermodynamic functions of the synthesized compound.

Synthesis, crystal structure and high-temperature heat capacity of substituted apatites Pb-=SUB=-9-=/SUB=-R(GeO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-(VO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=- (R=Tb, Dy, Ho)

“…Such a substitution allows both for changing the properties of the already known compounds with the apatite structure and for making new materials [16,17]. Thus, for instance, partial substitution of lead in apatite Pb 5 (GeO 4 )(VO 4 ) 2 (or Pb 10 (GeO 4 ) 2 (VO 4 ) 4 ) by rare earth elements (REE) provides compounds with the general formula Pb 10−x R x (GeO 4 ) 2+x (VO 4 ) 4−x (Rrare earth element, x takes on values from 0 to 3) [13,[18][19][20][21][22][23][24][25], and by bismuth -Pb 10−x Bi x (GeO 4 ) 2+x (VO 4 ) 4−x [26]. It should be noted that the properties of apatites Pb 10−x R x (GeO 4 ) 2+x (VO 4 ) 4−x have been poorly studied, while the available data mainly pertains to epy studies of their crystal structure.…”

“…We have obtained the heat capacity data only for the apatites of this class which contain La [19,20,22,25], Pr [23,25], Nd [21,25], Eu [24], Sm [25]. The available published data about thermodynamic properties pertains to other compounds with the apatite structure (fluor-, chlor-and hydroxyapatites) [27,28].…”