Heat-capacity measurements and absolute entropy of ɛ-Mg2PO4OH

The low-temperature heat capacity of ɛ-Mg2PO4OH was measured between 10 and 400 K by adiabatic calorimetry. No phase transition was observed over this temperature range. A relative enthalpy increment of 22,119 J mol−1 and an absolute entropy value of 127.13±0.25 J mol−1 K−1 at 298.15 K are derived from the results. The low-temperature heat-capacity data are compared with the DSC data obtained from 143 K to 775 K and show marginal differences in the common temperature range. The latter data are fitted by the polynomial % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4qamaaBa % aaleaacaWGWbaabeaakiabg2da9maacmaabaGaaG4maiaaigdacaaI % 2aGaaiOlaiaaiAdacaaIYaGaeyOeI0IaaGOmaiaaiMdacaaI1aGaaG % 4naiaaykW7caWGubWaaWbaaSqabeaacqGHsislcaaIWaGaaiOlaiaa % iwdaaaGccqGHsislcaaI1aGaaGOnaiaaiodacaaIZaGaaGynaiaaic % dacaaMc8UaamivamaaCaaaleqabaGaeyOeI0IaaGOmaaaakiabgUca % RiaaiMdacaaI1aGaaGynaiaac6cacaaI1aGaaGynaiabgEna0kaaig % dacaaIWaWaaWbaaSqabeaacaaI1aaaaOGaaGPaVlaadsfadaahaaWc % beqaaiabgkHiTiaaiodaaaaakiaawUhacaGL9baacaqGkbGaaGPaVl % aabUeadaahaaWcbeqaaiabgkHiTiaaigdaaaGccaaMc8UaaeyBaiaa % b+gacaqGSbWaaWbaaSqabeaacqGHsislcaaIXaaaaOGaaiilaaaa!6CC9! \[ C_p = \left\{ {316.62 - 2957\,T^{ - 0.5} - 563350\,T^{ - 2} + 955.55 \times 10^5 \,T^{ - 3} } \right\}{\text{J}}\,{\text{K}}^{ - 1} \,{\text{mol}}^{ - 1} , \] which allows extrapolation to high temperatures.