Structural and compositional data of maya pottery samples from Lake Petén Itzá, Guatemala: Central America

In this data article, we present the spectroscopic structural data of the pottery samples collected from Petén Itzá, Guatemala. Detailed Fourier transmission infrared, powder X-ray diffraction, scanning electron microscopy coupled to electron dispersive X-ray diffraction, and thermal gravimetric analysis/differential thermal gravimetric analysis (FTIR, PXRD, SEM/EDX, and TGA/DTGA) were discussed in the research article titled “Comprehensive Structural and Compositional Investigation of Maya Pottery Sherds from Lake Petén Itzá, Guatemala, Central America” (Onchoke et al. 2020 [1]). The FTIR, XRD profiles and composition of pottery from Petén Itzá, Guatemala are presented. This data is important and useful for further understanding of the structural composition of pottery sherds used by Maya people of Guatemala. In addition, the TGA/DTGA profiles provide information on the content of the losses upon heating and offers supportive evidence to the spectroscopic data studied.


a b s t r a c t
In this data article, we present the spectroscopic structural data of the pottery samples collected from Petén Itzá, Guatemala. Detailed Fourier transmission infrared, powder X-ray diffraction, scanning electron microscopy coupled to electron dispersive X-ray diffraction, and thermal gravimetric analysis/differential thermal gravimetric analysis (FTIR, PXRD, SEM/EDX, and TGA/DTGA) were discussed in the research article titled "Comprehensive Structural and Compositional Investigation of Maya Pottery Sherds from Lake Petén Itzá, Guatemala, Central America" (Onchoke et al. 2020 [1] ) . The FTIR, XRD profiles and composition of pottery from Petén Itzá, Guatemala are presented. This data is important and useful for further understanding of the structural composition of pottery sherds used by Maya people of Guatemala. In addition, the TGA/DTGA profiles provide information on the content of the losses upon heating and offers supportive evidence to the spectroscopic data studied.  Table   Subject Analytical Chemistry Specific subject area Analytical Archaeology Type of data Table, graph, figure How data was acquired (a) Fourier Transform Infrared (FTIR, Perkin Elmer Station 100 Inc., USA) was used for infrared analysis. (b) A Bruker AXS D8 Advance diffractometer equipped with an X-ray tube (Cu K α radiation: λ = 1.54060 Å , 40 kV, and 40 mA) using a Ni filter and one-dimensional LynxEye detector at scanning speed of 2 °/min and 0.0125 °step sizes and a 1s/step. (c) A JEOL-JSM 6100 scanning electron microscope equipped with a Horiba scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) was used. (d) A Perkin Elmer thermogravimetric and differential thermogravimetric analysis (TGA/DTGA) were performed with thermogravimetric simultaneous thermal analyzer (STA 60 0 0) at 20 °C/min heating rates in a nitrogen atmosphere in the range 34 °C -10 0 0 °C.

Data format
Raw data, analyzed Parameters for data collection (a) Power X-ray Diffraction (PXRD) analysis: Pottery samples obtained from Lake Petén Itzá, Guatemala were crushed, air dried, and ground to fine powder. (b) Fourier Transform infrared (FTIR) Analysis: The Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) spectra in the 230 -40 0 0 cm −1 region was acquired on an abrasive pad (4 cm −1 resolution) with Perkin Elmer Spectrum 100 spectrometer equipped with a Ge/CsI beam splitter and a DTGS detector. (c) SEM/EDX analysis: SEM micrographs and their elemental composition were acquired with use of a JEOL-JSM 6100 scanning electron microscope.
Description of data collection Forty-two pottery sherds were spectroscopically characterized and their crystalline phases determined. The powder diffraction file was acquired using Bruker AXS DIFFRAC.EVA program [2] . The fitted line profiles, peak search methods, and indexing of the lines were used to calculate the mineral identification via comparisons with the diffraction patterns with TOPAS program [3] .

Value of the Data
• The spectral data provided here is valuable for referencing, identification of crystalline phases, and differentiation between the pottery samples from sites around the world.
• The data provides important information for identification of elemental compositions in pottery sherds and samples. • The powder X-ray diffraction (PXRD) patterns are important for the identification of crystalline phases in pottery, and for comparisons to other archaeological samples.

Data Description
In this study, pottery sherds from Lake Petén Itzá, Guatemala, Central America ( Fig. 1 adapted from Ref # [4] ) were investigated for their composition. The data in this paper presents spectroscopic information on FTIR ( Fig. 2 ), SEM/EDX ( Figs. 3 and 4 , Table 1 ), the approximate compositions, d-spacings and hkl patterns ( Tables 2 , 3 , and 4 ). Fig. 5 depicts sample TGA/DTGA thermograms of select samples 1.12 and 1.17 showing mass losses at different temperatures in the range 33 -10 0 0 °C. The raw data for FTIR graphs, EDX spectra, and TGA representing Figs. 2 , 4 , and 5 can be found in the Supplementary Excel file titled Raw Data FTIR graphs, Raw EDX data graphs, and Raw data TGA graphs. Map of Guatemala; Picture adopted from Ref # [4] . Reprinted with permission from Elsevier publisher. Elsevier License for permission to re-use in a journal article was granted from the Elsevier publisher.

Experimental Design, Materials and Methods
The experimental methods and procedures that allowed the data here presented are described in References # [1 , 5-7] and cited references therein. Here, only the protocols for FTIR, PXRD, SEM morphological analysis, and TGA is provided, giving a large number of experimental details, usually omitted in research articles due to the words limit.

Study site and collection of pottery samples
The 42 samples (numbered 1.01, 1.02, 1.03, ……….1.42) that were analyzed in this study were collected from four sites of Lake Petén Itzá, Guatemala, Central America; namely, Flores, Zacpetén, Ixlú, and Nixtun Ch'ich' ( Fig. 1 ). The samples were tagged with their exact location and the date notating when collected (as shown in Supplementary Information Table in Ref. #1). The samples exhibited a variety of colors; tan, red, and grey (as shown in Ref # [1] ) while other pieces exhibited combinations of these colors.

Preparation of samples and analysis
Pottery samples were crushed to a fine consistency powder using a teflon mortar and pestle.

Fourier Transform Infrared (FTIR) analysis
An adequate concentrated layer of sample was spread on an abrasive pad and slid into the Perkin-Elmer Diffuse Reflectance Accessory. A background scan was acquired prior to acquisition of sample spectral data. In contrast to spectral data acquired via abrasive pads, energy sticks yielded absorption peaks of low intensity. A Perkin Elmer Station 100 with a CsI beam splitter

Powder x-ray diffraction (PXRD) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) analysis
Powder XRD analysis was performed in the 2 θ range of 2 °-90 °on a Bruker AXS D8 Advance diffractometer equipped with an X-ray tube (Cu K α radiation: λ = 1.54060 Å , 40 kV, and 40 mA) using a Ni filter equipped with a one-dimensional high-speed energy-dispersive LYNXEYE XE-T detector at scanning speed of 2 °/min and 0.0125 °step sizes and a 1s/step.
The crystalline structure peaks were identified using the software TOPAS [3] . Samples were analyzed against 120 crystal structures in two batches of 50 each. Crystalline phases with abundance < 1.0% were removed. The pooled spectra were analyzed a second time and crystals under 1.0% were removed. After analysis of 120 crystal structures and the removal of low crystalline phases, a comprehensive list of pooled crystals was created with percentages ≥ 0.5%. Select powder XRD patterns (reported in Ref # [1] ) and their hkl values and the crystalline phases present in pottery samples are presented in Tables 2 , 3 , and 4 for representative samples numbered 1.01, 1.02 and 1.03).
A Hitachi S2300 SEM was used to obtain micrographs. To minimize electrical charging, samples were sputter coated with Pd/Au. A JEOL-6100 SEM/EDX attachment and a tungsten filament was used to acquire sample composition. The detector (SiriusSD) is based on Silicon drift sensor technology and was kept at -20 ˚C. The working distance and voltages used were set at 15 mm, and 20 kV, respectively. An analysis period of 120 seconds was run per sample in order to lower the signal to noise ratio. Fig. 3 A, 3 B, 3 C, and 3 D depict SEM micrographs for selected samples numbered 1.13, 1.24, 1.31, and 1.35.

Morphological characterization of pottery samples
The pottery sherds were air dried, crushed with mortar and pestle, and analyzed with JEOL-JSM 6100 scanning electron microscope equipped with a Horiba energy dispersive X-ray spectroscopy (SEM/EDX) with an accelerating voltage of 15 kV. The surface morphology, particle diameters of samples were measured at X30 0, and X40 0 magnifications ( Fig. 3 A, Table 1 .

Thermogravimetric Analysis (TGA) analysis
Approximately 20 mg of finely crushed pottery sample was placed onto a sample holder cup. A Perkin Elmer TGA thermogravimetric simultaneous thermal analyzer (STA 60 0 0) at 20 °C/min heating rates in a nitrogen atmosphere in the range 33 °C -10 0 0 °C. Fig. 5 depicts the TGA and DTGA graphs of representative samples numbered 1.17, and 1.39.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.